NUNC COGNOSCO EX PARTE TRENT UNIVERSITY LIBRARY £ r. x. MOSSES AND FERNS THE STRUCTURE & DEVELOPMENT OF THE MOSSES & FERNS ( A R CHE G ONI A TAT) DOUGLAS HOUGHTON CAMPBELL, Ph.D. PROFESSOR OF BOTANY IN THE LELAND STANFORD JUNIOR UNIVERSITY JLonDon MACMILLAN AND CO. AND NEW YORK 1895 All rights resented ur O S' 3 V Digitized by the Internet Archive in 2019 with funding from Kahle/Austin Foundation https://archive.org/details/structuredevelopOOOOcamp PREFACE Ever since the appearance of Hofmeister’s remarkable investi¬ gations upon the Archegoniatae, the ever-increasing list of works upon these plants has borne witness to the interest felt by botanists in their structure and development. From time to time the results of these investigations have been collected^ but for the most part this has been done in general text-books, where want of space has naturally made it impossible, often, to give much more than a mere summary of results. The last ten years have been especially noteworthy, not only for the number of investigations upon the Archegoniates, but for the extension of our knowledge to many forms which were hitherto but very imperfectly known. These results have come from two sources : first, the extension of the field of research to the Tropics, through the establishment there of experiment -stations and properly equipped laboratories in connection with botanical gardens ; second, the advances in histological methods, especially the use of the microtome in embryological studies, which have made possible the accurate determination of many important structural details hitherto but very unsatisfactorily made out. The application of these more exact methods of research have made necessary, also, a careful review of the results of earlier investigations, and the correction of mistakes due to imperfect manipulations. The results of these later researches have only begun to find their way into the text-books, and the present work was undertaken mainly for the purpose of presenting, in somewhat detailed form, a resume of the substance of the great mass of literature upon the subject which has accumulated, and much of 148772 VI MOSSES AND FERNS which is necessarily out of reach of the many botanical workers who have not access to the great libraries. Various papers, published by the author from time to time, have served as the basis of the work, and these have been supplemented by a somewhat extended series of observations upon representatives of most of the groups of the Archegoniates, the results of which are now published for the first time. It is hoped that the result is a fairly comprehensive statement of our present knowledge of the comparative morphology of the Muscineae and Pteridophyta. Except where otherwise stated, the drawings were made by the author from his own preparations, and the majority were prepared expressly for this work. In view of the extremely unsettled state of botanical nomenclature at the present time, it was thought best to adopt a somewhat conservative attitude, and for the most part the names employed in the text are those which have long been familiar to the botanical student. Various departures from the generally accepted arrangement of the orders and families have been made, the reasons for which are set forth at sufficient length in the text. The author wishes to express his thanks to the many botanists both at home and abroad to whom he is indebted for assistance, both in the form of materials and information, with¬ out which the work would have been impossible. Especial thanks are due Professor W. Carruthers, through whose courtesy the great botanical collections and libraries of the British Museum at South Kensington were placed at his disposal. He is also under great obligation to Professor F. O. Bower for the advance sheets of recent important papers, which made it possible to complete the latter chapters much more satisfactorily than otherwise could have been done. DOUGLAS HOUGHTON CAMPBELL. Stanford University, California, March 1S95. CONTENTS CHAPTER I PAGE Introduction ....... 1 CHAPTER II Muscine/e (Bryophyta) — Hepatic/e — March anti ace/e . 8 CHAPTER III MARCHANTIE/E . . • • ■ • -42 CHAPTER IV The Jungermanniace/e . . ■ • • • 7i CHAPTER V The Anthocerote^e . • • • • 1 1 4 CHAPTER VI The Mosses (Musci) : Sphagnace^e — Andre/Eace^e . ■ 1S2 CHAPTER VII 1 8o The Bryine/E MOSSES AND FERNS viii CHAPTER VIII PAGE The Pteridophyta — Ophioglossace^e . . . .218 CHAPTER IX MARATTIACEjE - 1 SOETACEAD ..... 254 CHAPTER X FlLICINEiE LePTOSPORANGIATAS ..... 302 CHAPTER XI Classification of the Homosporous Leptosporangiat^e . 338 CHAPTER XII Leptosporangiat^; Heterospore^e (Hydropterides) . . 378 CHAPTER XIII Equisetine^e ....... 422 CHAPTER XIV Lycopodinea; . . . . . .461 CHAPTER XV Summary and Conclusions ..... 508 BIBLIOGRAPHY ..... COI INDEX 535 CHAPTER I INTRODUCTION UNDER the name Archegoniatae are included a large number of plants which, while differing a good deal in many structural details, still agree so closely in their essential points of structure and development as to leave no room for doubting their close relationship. Besides the Bryophytes and Pteri- dophytes, which are ordinarily included under this head, the Gymnospermae or Archespermae might very properly be also embraced here, but we shall use the term in its more restricted meaning. The term Archegoniatse has been applied to these plants because the female reproductive organ or archegonium is closely alike, both in origin and structure, in all of them. This is a multicellular body, commonly flask -shaped, and either entirely free or more or less coherent with the tissues of the plant. In all cases there is an axial row of cells developed, of which the lowest forms the egg. The others become more or less completely disorganised and are discharged from the archegonium at maturity. Among the Algae there is no form at present known in which the female organ can be certainly compared to the archegonium, although the oogonium of the Characeae recalls it in some respects. The antheridium or male organ of the Archegoniatae, while it shows a good deal of similarity in all of them, still exhibits much more variation than does the archegonium, and is more easily comparable with the same organ in the Algae, especially the Characeae. Like the archegonium it may be B 2 MOSSES AND FERNS chap. entirely free, or even raised on a long pedicel ; or it may be completely sunk in the tissue of the plant, or even be formed endogenously. It usually consists of a single outer layer of cells containing chlorophyll, and these enclose a mass of small colourless cells, the sperm cells, each of which gives rise to a single ciliated spermatozoid. The development of the latter is very uniform throughout the Archegoniatae, and differs mainly from the same process in the higher green Algae, especially the Characeae, in the larger amount of nuclear substance in the spermatozoids of the former. Fertilisation is only effected when the plants with ripe sexual organs are covered with water. The absorption of water by the mature sexual organs causes them to open, and then, as the spermatozoids are set free, they make their way through the water by means of their cilia and enter the open archegonium, into which they penetrate to the egg. The sexual cells do not differ essentially from those of the higher Algae, and point unmistakably to the origin of the Arche¬ goniatae from similar aquatic forms. Indeed all of the Archegoniatae must still be considered amphibious, inasmuch as the gametophyte or sexual plant is only functional when partially or completely submerged. Non-sexual gonidia are known certainly only in Aneura, one of the lower Liverworts, but special reproductive buds or gemmae, both unicellular and multicellular, are common in many forms. A very marked characteristic of the whole group is the sharply-marked alternation of sexual and non-sexual stages. The sexual plant or gametophyte varies much in size and complexity. It may be a simple flat thallus comparable in structure to some Algae, and not superior to these in com¬ plexity so far as the vegetative parts are concerned. In others it becomes larger and shows a high degree of differentiation. Thus among the Liverworts the Marchantiaceae, while the gametophyte still retains a distinctly thalloid form, still show a good deal of variety in the tissues of which the thallus is composed. In others, eg. the true Mosses, the gametophyte has a distinct axis and leaves, and in the higher ones the tissues are well differentiated for special functions. The gametophyte itself may show two well-marked phases, the piotonema and the gametophore. The former is usually I INTRODUCTION o filamentous, and arises directly from the germinating spore ; and upon the protonema, as a special branch or bud, the much more complex gametophore is borne. Often, however, as in many thallose Liverworts and Pteridophytes, the protonema is not clearly distinguishable from the gametophore, or may be completely suppressed. In the Pteridophytes the gametophyte is, as a rule, much simpler than in the Bryophytes, resembling most nearly the less specialised forms of the latter. In the so- called heterosporous Pteridophytes the gametophyte becomes extremely reduced and the vegetative part almost entirely suppressed, and its whole cycle of development may, in extreme cases, be completed within twenty-four hours or even less. The non-sexual generation, or “ sporophyte,” arises normally from the fertilised egg, but may in exceptional cases develop as a bud from the gametophyte. In its simplest form all the cells of the sporophyte, except a single layer upon the out¬ side, give rise to spores, but in all the others there is developed a certain amount of vegetative tissue as well, and the sporo¬ phyte becomes to a limited extent self-supporting. In the higher Bryophytes the sporophyte sometimes exceeds in size the gametophyte, and develops an elaborate assimilative system of tissues, abundantly supplied with chlorophyll and having an epidermis with perfect stomata ; but even the most complex moss-sporogonium is to a certain extent dependent upon the gametophyte, with which it remains in close connection by means of a special absorbent organ, the foot. In these highly developed sporogonia the sporogenous tissue occupies but a small space, by far the greater part of the tissue being purely vegetative. In the Pteridophytes a great advance is made in the sporophyte beyond the most complex forms found among the Bryophytes. This advance is twofold, and consists both in an external differentiation and a more perfect development of the tissues. The earliest divisions of the embryo resemble very closely those of the Bryophyte sporogonium, but at an early stage four distinct organs are usually plainly distinguishable, viz. stem, leaf, root, and foot. The last corresponds in some degree to the same organ in the moss-sporogonium, and like it serves as an absorbent organ by which the young sporophyte is supplied with nourishment from the gametophyte. In short, 4 MOSSES AND FERNS CHAP. the young sporophyte of the Pteridophyte, like that of the Bryophyte, lives for a time parasitically upon the gametophyte. Sooner or later, however, the sporophyte becomes entirely independent. This is effected by the further growth of the primary root, which brings the young sporophyte into direct communication with the earth. The primary leaf, or cotyledon, enlarges and becomes functional, and new ones arise from the stem apex. Usually by the time this stage is reached the gametophyte dies and all trace of it soon disappears. In some of the lower forms, however, the game¬ tophyte is large and may live for many months, or even years, when not fecundated, and even when the sporophyte is formed, the prothallium (gametophyte) does not always die immediately, but may remain alive for several months. The spore-forming nature of the sporophyte does not manifest itself for a long time, sometimes many years, so that spore-formation is much more subordinate than in the highest Bryophytes. With few excep¬ tions the spores are developed from the leaves and in special organs, sporangia. In the simplest cases, i.e. Ophioglossum , the sporangia are little more than cavities in the tissue of the sporiferous leaf, and project but little above its surface. Usually, however, the sporangia are quite free from the leaf and attached only by a stalk. These sporangia are in the more specialised forms of very peculiar and characteristic structure, and are of great importance in classification. Corresponding to the large size and development of special organs in the sporophyte of the Pteridophytes, there is a great advance in the specialisation of the tissues. All of the forms of tissue found in the Spermaphytes occur also among the Pteridophytes, which indeed, so far as the character of the tissues of the sporophyte is concerned, come much nearer to the former than they do to the Bryophytes. This is especially true of the vascular bundles, which in their complete form are met with first in the sporophyte of the Pteridophyta. In size, too, the sporophyte far exceeds that of the highest Mosses ; while in these the sporogonium never exceeds a few centimetres in extreme height, in some Ferns it assumes tree-like pro¬ portions with a massive trunk i o to is metres in height with leaves 5 to 6 metres in length. In the formation of the spores all of the Archegoniatae show great uniformity, and this extends, at least as regards I INTRODUCTION 5 the pollen spores, to the Spermaphytes as well. In all cases the spores arise from cells which at first .form a solid tissue arising from the division of a single primary cell, or group of cells (Archesporium). These cells later become more or less completely separated, and each one of these so-called “ spore mother cells,” by division into four daughter cells, forms the spores. The young spores are thin walled, but later the wall becomes thicker and shows a division into two parts, one inner larger, which generally shows the cellulose reaction and is called the endospore (intine), and an outer more or less cuticularised coat, the exospore (exine). In addition a third outer coat (perinium, epispore) is very generally present. As the spore ripens there is developed within it reserve food materials in the form of starch, oil, and albuminous matter, and quite frequently chlorophyll is present in large quantity. Some spores retain their vitality but a short time, those of most species of Equisetum and Osmunda , for example, germinating with difficulty if kept more than a few days after they are shed, and very soon losing their power of germination com¬ pletely. On the other hand, some species of Marsilia have spores so tenacious of life that they germinate perfectly after being kept for several years. From the germinating spore arises the gametophyte bear¬ ing the sexual organs. Both archegonia and antheridia may be borne upon the same plant, or they may be upon separate ones. From the fertilised egg within the archegonium is produced the sporophyte or non-sexual generation, and from the spores which it produces arise the sexual individuals again, thus completing the cycle of development. On comparing the lower Archegoniates with the higher ones, it is at once evident that the advance in structure consists mainly in the very much greater development of the sporophyte. In the Bryophytes, as a class, the gametophyte is more important than the sporophyte, the latter being, physiologically, merely a spore-fruit, which in many forms, i.e. Sphagnum , is of relatively rare occurrence. The gametophyte in such forms is perennial, and the same plant may produce a large number of sporogonia, and at long intervals. The sporophyte in such forms is small and simple in structure, and its main function is spore formation, as it has but little power of independent growth. In the Pteridophytes, on the other hand, the gameto- 6 MOSSES AND FERNS CHAP. phyte (prothallium) rarely produces more than one sporophyte, and as soon as this, by the formation of a root and leaf, becomes self-supporting, the gametophyte dies. In short, the sole function of the latter in most of them is to support the sporophyte until it can take care of itself. When the lower Pteridophytes are compared with the more specialised ones, a similar difference is found. In the lower forms, like the Marattiacese and Equisetacese, the gametophyte is relatively large and long-lived, and closely resembles certain Liverworts. In these forms a considerable time elapses before sexual organs are produced, and in artificial cultures of the Marattiacese a year or more sometimes passes before archegonia are formed. These prothallia, too, multiply by budding, much as the Liverworts do. In case no archegonia are fecundated the prothallium may grow until it reaches a length of three or four centimetres, and resembles in a most striking manner a thalloid Liverwort. In such large prothallia it is not unusual for more than one archegonium to be fecundated, although usually only one of the embryos comes to maturity, and the prothallium may continue to live for some time after the sporophyte has become independent. Usually, however, as soon as an arche¬ gonium is fertilised, the formation of new ones ceases, and as soon as the sporophyte is fairly rooted in the ground the prothallium dies. In most of the lower Pteridophytes the prothallia are monoecious, but in the more specialised ones are markedly dioecious. When this is least marked the males and females differ mainly in size, the latter being decidedly larger ; in the more extreme cases the difference is much more pronounced and is correlated with a great reduction in the vegetative part of the gametophyte in both males and females. This reaches its extreme phase in the so-called heterosporous forms. In these the sex of the gametophyte is already indicated by the character of the spore. Two sorts of spores are produced, large and small, which produce respectively females and males. In all of the heterosporic Pteridophytes the reduction of the vegetative part of the gametophyte is very great, especially in the male plants. Plere this may be reduced to a single quite functionless cell, and all the rest of the plant is devoted to the formation of the single antheridium. In the female plants the reduction is not so great ; and although sometimes but one I INTRODUCTION 7 archegonium is formed, there may be in some cases a consider¬ able number, and owing to the large amount of nutritive material in the spore, in case an archegonium is not fertilised, the prothallium, even if it does not form chlorophyll, may grow for a long time at the expense of the food materials that normally are used by the developing embryo. In strong contrast to the slow growth and late development of the reproductive organs in the homosporous forms, most of the heterosporous Pteridophytes germinate very quickly. The Marsiliaceae, in which the female prothallium is extremely reduced, show the opposite extreme. Here the whole time necessary for the germination of the spores and the maturing of the sexual organs may be less than twenty-four hours, and within three or four days more the embryo is completely developed. That heterospory has arisen independently in several widely separated groups of Pteridophytes is plain. The few genera that still exist are readily separable into groups that have comparatively little in common beyond possessing two sorts of spores ; but each of these same forms shows much nearer affinities to certain widely separated homosporous groups. In some of the heterosporous forms the first divisions in the germinating spore take place while it is still within the sporangium, and may begin before the spore is nearly fully developed. In other cases the sporangia become detached when ripe, and the spore (or spores), still surrounded by the sporangium, falls away from the sporophyte before germination begins. In these respects the heterosporous Pteridophytes show the closest analogy with the similar processes among the lower Spermaphytes, where it has been shown in the most conclusive manner that the ovule with its enclosed embryo-sac is the exact morphological equivalent of the macrosporangium of Selaginella or Azolla, for example, and that the seed is simply a further development of the same structure. CHAPTER II MUSCINEzE (BRYOPHYTA) HEPATIC^- — MARCH ANTI ACEHL The first division of the Archegoniatae, the Muscineae or Bryophyta, comprises the two classes, Hepaticae or Liverworts, and the Musci or Mosses. In these as a rule the gametophyte is much more developed than the sporophyte, and indeed in many forms the latter is very rarely met with. They are plants of small size, ranging in size from about a millimetre in length to 30 centimetres or more. A few of them are strictly aquatic, i.e. Riella and Ricciocarpus among the Hepa¬ ticae, and Fontinalis of the Mosses ; but most of them grow upon a solid substratum. A favourite position for many is the trunks of trees or rocks. Many others grow upon the earth. They vegetate only when supplied with abundant moisture, and some forms are very quickly killed if allowed to become dry ; but those species which grow in exposed places may be completely dried up without suffering, and some of those that inhabit countries where there are long dry periods may remain in this condition for months without losing their vitality, reviving immediately and resuming growth as soon as they are supplied with the requisite moisture. 1 he germinating spores usually produce a more or less well-marked “ protonema,” from which the gametophore arises secondarily. I he protonema sometimes is persistent and forms a dense conferva-like growth, but more commonly it is tran¬ sient and disappears more or less completely after the gametophore is formed. No absolute line, however, can be drawn between protonema and gametophore, as the former may arise secondarily from the latter, or even from the sporophyte. With very few exceptions, i.e. Buxbaumia, the CH. II M U S CINEsE — H EPA TICJE — MARCH ANTI A CEsE 9 gametophyte of the Muscineae is abundantly supplied with chlorophyll, and therefore capable of entirely independent growth. No true roots are found, but root-hairs are generally present in great numbers, and these serve both to fasten the plant to the substratum and also to supply it with nutriment. The form of the gametophyte varies much. In the simplest Hepaticae, like Aneura and Pellia, it is a flat, usually dichotomously branched thallus composed of nearly or quite uniform cells, without traces of leaves or other special organs, hrom this simplest type, which is quite like certain Algae, differentiation seems to have proceeded in two directions ; in the first instance the plant has retained its thalloid character, but there has been a specialisation of the tissues, as we see in the higher Marchantiaceae. In the second case the differ¬ entiation has been an external one, the thalloid form giving place to a distinct leafy axis. This latter form reaches its completest expression in the higher Mosses, where it is accom¬ panied by a high degree of specialisation of the tissues as well. The growth is usually from a single apical cell, which varies a good deal in form among the thalloid Hepaticae, but in the foliose Hepaticae and Mosses is with few exceptions a three- sided pyramid. The gametophyte of the Muscineae frequently is capable of rapid multiplication, which may occur in several ways. Where a filamentous protonema is present this branches ex¬ tensively, and large numbers of leafy axes may be produced as buds from it. Sometimes these buds are arrested in their development and enter a dormant condition, and only ger¬ minate after a period of rest. Another very common method of multiplication is for the growing ends of the branches of a plant to become isolated by the dying away of the tissues behind them, so that each growing tip becomes the apex of a new plant. Very common in the Hepaticae, but less so in the Mosses, is the formation of gemmae or special reproductive buds. These are produced in various ways, the simplest being the separation of single cells, or small groups of cells, from the margins of the leaves. In the case of Aneura multifida they are formed within the cells and discharged in a manner that seems to be identical with that of the zoospores of many Algae. Again, multicellular gemmae of peculiar form occur in several of the Hepaticae, e.g. Blasia, Marchantia , where they occur in IO MOSSES AND FERNS CHAP. special receptacles, and among the Mosses similar ones are common in Tetraphis and some other genera. The archegonia of all the Muscineae agree closely in their earlier stages, but differ more or less in the different groups at maturity. In all cases the archegonium arises from a single superficial cell, in which three vertical walls are formed that intersect so as to form an axial cell and three peripheral ones. From the axial cell develop the egg, canal cells, and cover cells of the neck, and from the peripheral cells the wall of the venter and the outer neck cells. In all Muscineai except the Antho- cerotese the archegonium mother cell projects above the sur¬ rounding cells, but in the latter the mother cell does not project at all, and the archegonium remains completely sunken in the thallus. In all other forms the archegonium is nearly or quite free, and usually provided with a short pedicel. This is especi¬ ally marked in the Mosses, where the lower part of the arche¬ gonium is as a rule much more massive than in the Hepaticse. The most marked difference, however, between the arche¬ gonium of the Hepaticae and Mosses is in the history of the cover cell or uppermost of the axial row of cells of the young archegonium. This in the former divides at an early period into four nearly equal cells by vertical walls, the resulting cells either remaining undivided, or undergoing one or two more divisions ; but in the Mosses this cell functions as an apical cell, and to its further growth and division the whole growth of the neck is due. The antheridia, except in the Anthocerotese, also arise from single superficial cells, and while they differ much in size and form, are alike in regard to their general structure. The antheridium always consists of two parts : a stalk or pedicel, which varies much in length, and the antheridium proper, made up of a single layer of superficial cells and a central mass of small sperm cells. 1 he former always contain chloroplasts, which often become red or yellow at maturity. The sperm cells have no chlorophyll, but abundant protoplasm and a large nucleus, which latter forms the bulk of the body of the sper- matozoid found in each sperm cell of the ripe antheridium. 1 he spermatozoids are extremely minute filiform bodies, thicker behind and provided with two fine cilia attached to the forward end. Adhering to the thicker posterior end there may usually be seen a delicate vesicle, which represents the II M US Cl ZV EsE — HE PA TICjE—MA RCHA NTIA CEsE i i remains of the cell contents not used up in the formation of the spermatozoid. When the ripe sexual organs are placed in water their outer cells absorb water rapidly and become strongly distended, while the central cells, i.e. the canal cells of the archegonium, and the sperm cells, whose walls have become mucilaginous, have their walls dissolved. The swelling of the mucilage derived from the walls of the central cells, combined with the pressure of the strongly distended outer cells, finally results in the bursting open of both archegonium and antheridium. In the former, by the forcing out of the remains of the canal cells an open channel is left down to the egg, which has been formed by the contracting of the contents of the lowest of the axial cells. In the antheridium the walls of the sperm cells are not usually completely dissolved at the time the anther¬ idium opens, so that the spermatozoids are still surrounded by a thin cell wall when they are first discharged. This soon is completely dissolved, and the spermatozoid then swims away. The substance discharged by the archegonium exer¬ cises a strong attraction upon the spermatozoids, which are thus directed to the open mouth of the archegonium, which they enter. Only a single one actually enters the egg, where it fuses with the egg-nucleus, and thus effects fertilisation. The egg immediately secretes a cellulose wall about itself, and shortly after the fusion of the nuclei is complete the first segmentation of the young embryo takes place. The origin of the sexual organs is from a single cell, but the position of this cell varies much. In the thalloid Hepaticae it is a superficial cell, formed from a segment of the apical cell either of a main axis or of a special branch. In most of the foliose Hepaticae and the Mosses, the apical cell of the shoot becomes itself the mother cell of an archegonium, and of course with this the further growth of the axis is stopped. The antheridia in the foliose Hepaticae are usually placed singly in the axils of more or less modified leaves, but in most Mosses the antheridia form a terminal group. Mixed with the sexual organs are usually found sterile hair-like organs, paraphyses, often of very characteristic forms. In the foliose Hepaticae and most Mosses, the archegonia are often surrounded by specially modified leaves, and in the former there is also an inner cup-like perichaetium formed from the tissue surrounding 12 MOSSES AND FERNS CHAP. the archegonia. In the thallose Hepaticae, both antheridia and archegonia are generally enclosed by a sort of capsule, similar to the perichaetium of the foliose forms formed by the growth of the tissue of the thallus immediately surrounding them. The Asexual Generation ( Sporophyte , Sporophore , Sporogonium ) The sporophyte of the Muscineae is usually known as the “ sporogonium,” and, as already stated, never becomes entirely independent of the gametophyte. After the first divisions are completed there is at an early period, especially in the Hepaticae, a separation of the spore-producing tissue or arche- sporium, all the cells of which may produce spores, as in Riccia and the Mosses, or a certain number form special sterile cells which either undergo little change and serve simply as nourish¬ ment for the growing Sphcerocarpus, or more commonly assume the form of elongated cells, — elaters, which assist in scattering the ripe spores. Classification Class I. Hepaticce ( Liverzvorts ) The protonema is either rudimentary or wanting, and not sharply differentiated from the gametophore. The game- tophore is, with the exception of Riella Haplomitrium and Calobryum , strongly dorsiventral, and may be either a (usually dichotomously) branched thallus or a stem with two or three rows of leaves. Non-sexual multiplication of the gametophyte by the separation of ordinary branches, or by special reproductive bodies, gonidia ( Aneura multifida ) or gemmae — (many foliose Jungermanniacea , Blasia, Marchantia, etc.). The sporogonium (except in Anthoceroteae) remains within the enlarged venter (Calyptra) of the archegonium until the spores are ripe. Before the spores are shed the sporogonium generally breaks through the calyptra by the elongation of the cells of the stalk or seta. All the cells of the archesporium may produce spores, or part of them may produce sterile cells or elaters. II M US CINE AH — HEP A TIC AH — MARCH ANTI A CEAI 13 CLASS II. Musci (Mosses)' The gametophyte shows a sharp separation into protonema and gametophore. The protonema arises primarily from the germinating spore, and may be either a flat thallus or more commonly an extensively branching confervoid growth. Upon this as a bud the gametophore arises. This has always a more or less developed axis about which the leaves are arranged in two, three, or more rows. A bilateral arrangement of the leaves is rare, and the stems branch monopodially. The asexual multiplication is by the separation of branches through the dying away of the older tissues, or less commonly by special buds or gemmae. Both stem and leaves have the tissues more highly differentiated than is the case in the Hepaticae. The archesporium is developed as a rule later than is the case in the Hepaticae, and within is a large central mass of tissue, the columella, which persists until the capsule is ripe. In most cases there is a large amount of assimilative tissue in the outer part of the capsule, and the epidermis at’ its base is provided with stomata. The growing embryo breaks through the calyptra at an early stage, and the upper part is in most cases carried up on top of the elongating sporogonium. In very much the greater number of forms the top of the capsule comes away as a lid (operculum). The Hepaticce The Hepaticae show many evidences of being a primitive group of plants, and for this reason a thorough knowledge of their structure is of especial importance in studying the origin of the higher plants, as it seems probable that all of these are derived from Liverwort-like forms. On comparing the Hepaticae with the Mosses one is at once struck with the very much greater diversity of structure shown by the former group, although the number of species is several times greater in the latter. On the one hand, the Hepaticae approach the Algae, the thallus of the simpler forms being but little more compli¬ cated than that of many of the higher green Algae. On the other hand, these same simpler Liverworts resemble in a most striking manner the gametophyte of the Ferns. The same 14 MOSSES AND FERNS CHAP. difference is observed in the sporophyte. This in the simplest Liverworts, eg. Riccia, is very much like the spore-fruit of Coleochoste , one of the confervoid green Algae ; on the other hand, the sporogonium of Anthoceros shows some most significant structural affinities with the lower Pteridophytes. The simplest form of the gametophyte among the Hepaticae is found in the thallose Jungermanniaceae and Anthoceroteae. In such forms as Aneura (Fig. 38) and Anthoceros (Fig. 55) the thallus is made up of almost perfectly uniform chlorophyll¬ bearing tissue, fastened to the earth by means of simple root -hairs. In forms a little more advanced, i.e. Metzgeria, Pallavicinia (Fig. 38), there is a definite midrib present. From this stage there has been a divergence in two directions. In one series, the Marchantiaceae, there has been a specialisa¬ tion of the tissues, with a retention of the thalloid form of the plant. In Riccia (Figs. 1-9) we find two clearly marked regions, a dorsal green tissue, with numerous air-spaces, and a ventral compact colourless tissue. In the higher Marchantiaceae (Fig. 16) this is carried still further, and the air-chambers often assume a definite form, and a distinct epidermis with characteristic pores is formed. In the Marchantiaceae also, ventral scales or leaf-like lamellae are developed, and root-hairs of two kinds are present. Starting again from the flat, simple thallus of Aneura (. Riccardia ), two other characteristic types are met with, the peculiar spiral thallus of Riella, and the leafy axis of the more specialised Jungermanniaceae. Between the latter and the strictly thallose forms are a number of interesting intermediate forms, like Blasia and Fossombronia, where the first indication of the two dorsal rows of leaves is met with ; and in Blast a at least the rudiments of the ventral row of small leaves (Amphigastria) usually found in the foliose forms are present. The tissues of the Liverworts are very simple, and consist for the most part of but slightly modified parenchyma. Occasionally ( Preissia ) thickened sclerenchyma - like fibres occur, but these are not common. Mucilage cells of various kinds are common. The secreting cells may be hairs on the ventral surface, and especially developed near the apex, where the mucilaginous secretion serves to protect against drying up ; or they may be isolated (. Marchantia ) or rows of cells (Cono- cephalus ) within the tissue of the thallus. In the Anthoceroteae II MUS CIN EEE — HEP A TICJE — MARCH A NT1A CE^E 15 stoma-like slits upon the ventral surface lead to cavities where great quantities of mucilaginous matter are secreted. The growth of the gametophore is usually due to the division of a single apical cell. In some of the thallose forms, eg. Marchantiaceae, Anthoceroteae, a single initial cell is not always to be recognised in the older thallus, but in these forms a single initial always appears to be present in the earlier stages. In the Jungermanniaceae, however, a single apical cell is always distinguishable, but varies a good deal in form in different genera, at least among the thalloid forms, or even in the same genus. Among the foliose Jungermanniaceae it always has the form of a three-sided pyramid. From the apical cell segments are cut off in regular succession, and the first divisions of the segments also show' much regularity, and often bear a definite relation to the tissues of the older parts. The Sexual Organs The archegonium is always traceable to a single cell, but the position of the mother cell is very different in different genera. In the simplest cases, eg. Riccia, Sphcerocarpus (Figs. 2, 29), the mother cell is formed from a superficial cell of one of the youngest dorsal segments of the apical cell, close to the growing point of an ordinary branch of the thallus, whose growth is in no way affected by the formation of archegonia. In such forms the archegonia stand alone, and about each is developed a sort of involucre by the growth of a ring of cells immediately surrounding the archegonium rudiment. In other cases the archegonia are found in groups, eg. Pallavicinia (Fig. 38), separated by spaces where no archegonia are found. Here each group of archegonia has a common involucre. In Aneura and most of the higher Marchantiaceae the archegonia are found in the same way, but upon special modified branches. In the foliose Jungermanniaceae the origin of the archegonia is somewhat different. Here they are formed upon short branches, where, after a small number of perichaetial leaves have been formed, the subsequent segments of the apical cell develop archegonia at once, and finally the apical cell itself becomes the mother cell of the last-formed archegonium, and, of course, with this the growth in length of the branch ceases. With the exception of the Anthoceroteae, where the arche- i6 MOSSES AND FERNS CHAP. gonium mother cell does not project at all, it quickly assumes a papillate form and is divided by a transverse wall into a basal cell, and an outer one from which the archegonium itself develops. The divisions in this outer cell are remarkably uniform. Three vertical walls are first formed, intersecting so as to enclose a central cell (Fig. 2, G). In this central cell a transverse wall next cuts off a smaller, upper cell (cover cell) from a lower one. Subsequently the three (or in the Jungermanniaceae usually but two) first - formed peripheral cells divide again vertically, and by transverse walls in all of the peripheral cells, and somewhat later in the central one also, the young archegonium is divided into two tiers, a lower one or venter, and an upper one, the neck (Fig. 2, F). The middle cell of the axial row, by a series of transverse walls, gives rise to the row of neck canal cells, and the lowermost o cell divides into two an upper one, the ventral canal cell, and a larger lower one, the egg. The antheridium shows very much greater diversity in its structure, and equally great difference in its position. The origin in the thallose forms is usually the same as that of the archegonium, and indeed where the two grow mixed together, as in many species of Riccia, it is sometimes difficult to distinguish them in their earliest stages. Usually, however, the antheridia are borne together, either on special branches ( Marchantia , species of Anetira), or they are produced in a special part of the ordinary thallus, which usually presents a papillate appearance (eg. Fimbriaria). In the foliose Junger¬ manniaceae the antheridia are often borne singly in the axils of slightly modified leaves, but in no case does the apical cell of the shoot become transformed into an antheridium. With the exception of the Anthoceroteae, where the antheridia are of endogenous origin, the antheridium, like the archegonium, arises from a single superficial cell. The first division usually divides the primary cell into a stalk cell and the body of the anther¬ idium. The first may remain very short and undergo but few divisions, or it may develop into a stalk of considerable length. The first division in the upper cell may be either transverse (Marchantiaceae, S phcerocarpus) or vertical (Junger¬ manniaceae). Later, by a series of periclinal walls, a central group of cells is separated from an outer single layer of cells. The latter divide only a few times, and develop chlorophyll, II MUS Cl NEAL — H EPA TICEE — MARCHA NTIA CEEE 1 7 which sometimes changes into a red or yellow pigment at maturity. The inner cells give rise to a very large number of sperm cells, which in most Hepaticm are extremely small, and consequently not well adapted to studying the development of the spermatozoids. In a few forms, however, they are larger ; and in P cilia especially, where the sperm cells are relatively large, the development has been carefully studied by Guignard,1 Buchtien,- and others of late years, as well as by many of the earlier observers, and a comparison with other Hepaticse shows great uniformity in regard to the origin and development of the spermatozoid. After the last division of the central cells the nuclei retain their flattened form, and thus the sperm cells remain in pairs, an appearance very common in the ripe antheridium of most Liverworts. Just before the differentiation of the body of the spermatozoid begins, the nucleus has the appearance of an ordinary resting nucleus, but no nucleolus can be seen. The first change is an indentation in the edge of the discoid nucleus, and this deepens rapidly until the nucleus assumes a crescent form. One of the ends is somewhat sharper and more slender than the other, and this constitutes the anterior end. As the body of the spermatozoid grows in length it becomes more and more homogeneous, the separate chromo¬ somes apparently fusing together as the body develops. The body of the spermatozoid increases in length until it forms a slender spiral band coiled in a single plane, lying parallel with the one in its sister cell. The full-grown spermatozoid in Pellia epiphylla has, accord¬ ing to Guignard,3 from three to four complete coils. Most Hepaticae have much smaller spermatozoids, and they have fewer coils than in Pellia. In all the Hepaticae the spermato¬ zoid is provided with two cilia, which sometimes exceed in length the body. There is still some disagreement as to their exact method of formation, but from the latest re¬ searches of Strasburger4 it seems probable that they arise as direct outgrowths of the forward end of the body of the spermatozoid, this pointed anterior portion not being nuclear in nature, but composed of what Strasburger calls “ kinoplasm.” They begin to form at an early stage in the development of the spermatozoid, and reach their full length 1 Guignard (i). “ Buchtien (i). 3 Guignard (i), p. 67. 4 Strasburger (8), pt. iv. p. 125. i8 MOSSES AND FERNS CHAP. before the body of the spermatozoid is complete. Usually when the spermatozoid escapes, it has attached to the coil a small vesicle which swells up more or less by the absorption of water. This vesicle is the remains of the cytoplasm of the cell, and may, perhaps, contain also some of the central part of the nucleus. Guignard 1 asserts that sometimes the cytoplasm is all used up during the growth of the spermatozoid, and that the free spermatozoid shows no trace of a vesicle. In the Ricciaceae and in Sphczrocarpus new archegonia continue to form even after several have been fertilised, so that numerous sporogonia develop upon the same branch of the thallus ; but in most Liverworts the fertilisation of an arche- gonium checks the further formation of archegonia in the same group, and only those that are near maturity at the time reach their full development ; and even if more than one archegonium of a group is fecundated, as a rule but one embryo comes to maturity. Unquestionably the lowest type of sporogonium is found in Riccia (Fig. 6). Here the result of the first divisions in the embryo is a globular mass of cells, which a little later shows a single layer of peripheral cells and a central mass of spore mother cells, all of which produce spores in the usual way. The sporogonium remains covered by the venter of the archegonium until the spores are ripe, and never projects above the surface of the thallus. The spores only escape after the thallus (or at least that part of it containing the sporogonia) dies and sets them free as it decays. In the genus Sphcerocarpus (Fig. 30), which may be taken to represent the next stage of development, we notice two points in which it differs from Riccia. In the first place there is a basal portion (foot), which is simply an absorbent organ, and takes no part in the production of spores. Secondly, only a part of the archesporium develops perfect spores. A number of the spore mother cells remain undivided, and serve simply to nourish the growing spores. In the majority of the Hepaticae the sporogonium shows, besides the foot and the capsule, an intermediate portion, the stalk or seta, which remains short until the spores are ripe, when, by a rapid elongation of its cells, the capsule is forced through the calyptra and the spores are discharged outside. In these forms, too, some of the cells of the archesporium remain undivided, and 1 Guignard (1), p. 66. II M USCINEsE — HEP A T1CJS-. MARCH ANTI A CEEE l9 very early are distinguished by their elongated shape from the young spore mother cells. These elongated cells later develop upon the inner surface of the cell wall peculiar spiral thickened bands, which are strongly hygroscopic. These peculiar fusiform cells, the elaters, are found more or less developed in all the Hepaticse except the lowest ones. The Anthocerotese differ very much from the other Hepaticse in the structure of the sporogonium, as they do in other respects. Here alone among Bryophytes the sporogonium may have unlimited growth, the development continuing as long as the gametophyte remains alive. While in the lowest genus, Notothylas, the growth is limited, and the spores and elaters occupy the greater part of the sporogonium, in Anthoceros the archesporium consists of but a single layer of cells surrounding a central cylindrical mass of tissue, the columella, and is separated from the outside of the capsule by several layers of cells. The outer tissue is rich in chlorophyll, and there is a well-developed epidermis with large stomata differing neither in origin nor structure from those of vascular plants. The foot is very large, and just above it is a zone of actively dividing cells which cause the growth in length of the sporogonium. The dehiscence of the sporogonium is different in the different orders. In the Ricciaceae and some Marchantiaceae the ripe sporogonium opens irregularly ; in a few cases (species of Finibriaria ) the top of the capsule comes off as a lid ; in most Jungermanniaceae the wall of the capsule splits vertically into four valves, and in the Anthoceroteae the sporogonium divides into two valves like a bean-pod. The spores are always of the tetrahedral type, i.e. the nucleus of the spore mother cell divides twice before there is any division of the cytoplasm, although this division may be indicated by ridges projecting into the cell cavity, and partially dividing it before any nuclear division takes place. The four nuclei are arranged at equal distances from each other near the periphery of the mother cell, and then between them are formed simultaneously cell walls dividing the globular mother cell into four equal cells having a nearly tetrahedral form. These tetrads of spores remain together until nearly full grown, or in a few cases until they are quite ripe. In the ripe spore two, sometimes three, distinct coats can be seen, the inner one (endospore, intine) of unchanged cellulose, the outer one 20 MOSSES AND FERNS CHAP. (exospore, exine) strongly cutinised and usually having upon the outside characteristic thickenings, ridges, folds, spines, etc. Where these thickenings are formed from the outside they constitute the third coat (perinium, epispore). The exospore is especially well developed in species where the spores are exposed to great heat or dryness, and which do not germinate at once. In those species that are found in cooler and moister situations, especially where the spores germinate at once, the exospore is frequently thin. The nucleus of the ripe spore is usually small. The cytoplasm is filled with granules, mostly albuminous in nature, with some starch and generally a great deal of fatty oil that renders the contents of the fresh spore very turbid. Some forms, especially the foliose Junger- manniaceae, have also numerous chloroplasts, but this is lacking usually in those forms that require a period of rest before germination. In Pellia and Conocephalus the first divisions in the germinating spore take place while the spores are still within the sporogonium. The germination of the spores begins usually by the forma¬ tion of a long tube (germ-tube, “ Keimschlauch ” of German authors), into which pass the granular contents of the spore. At the same time there may be formed a root-hair growing in a direction opposite to that of the germinal tube, although quite as often the formation of the first root-hair does not take place until a later period. If the spore does not contain chlorophyll before germination, it is developed at an early stage, before any cell-divisions occur. Often the formation of a germ-tube is suppressed and a cell surface or cell mass is formed at once, and all these forms may occur in the same species. The germination only takes place when the light is of sufficient intensity, and the amount of light is a very important factor in determining the form of the young plant. Thus if the light is deficient, the germ-tube becomes excessively long and slender, and divisions may be entirely suppressed. An excess of light tends to the development at once of a cell surface or cell mass. In the simpler thalloid forms the first few divisions in the young plant establish the apical cell, and we cannot properly speak of the gametophore as arising secondarily from a protonema ; in other cases, however, the young plant does arise as an outgrowth or bud from a protonema, which only rarely has the branching filamentous character of the Moss protonema. II MUS CINEjE — HEP A TIC EE — MA RCHA NTIA CEAE 21 Classification of the Hepatic.f: The Hepaticae are readily separated into the three following well-marked groups. Group I. Marchantiaceae. Group II. Jungermanniaceae. Group III. Anthoceroteae. The following diagnoses are taken, with some modifications, from Schiffner.1 Gro up /. Ma r chantia CEA£ Gametophyte always' strictly thallose, composed of several distinct layers of tissue, the uppermost or chlorophyll-bearing cells usually containing large air-spaces. The dorsal epidermis usually provided with pores, ventral surface with scales arranged in one or two longitudinal rows. Rhizoids of two kinds, with smooth walls, and papillate ; sexual organs, except in the lowest forms, united in groups which are often borne on special stalked receptacles. The first divisions of the embryo are arranged like the quadrants of a sphere. Sporogonium either with or without a stalk, and all the inner cells forming spores, or some of them producing elaters. No columella present. Fain. i. Ricciacece Chlorophyll-bearing tissue with or without air-chambers, and, where these are present, they never contain a special assimilative tissue. Epidermal pores wanting or rudimentary. Sexual organs immersed in open cavities upon the dorsal surface. Sporogonium without foot or stalk, and remaining permanently within the venter of the archegonium. All the cells of the archesporium producing spores. Fain. 2. Corsiniece Air-chambers well developed ; epidermis with distinct pores ; sexual organs in distinct groups, but the receptacles 1 Schiffner (i), p. 5- 22 MOSSES AND FERNS CHAP. always sessile ; sporogonium with a short stalk, producing besides the spores sterile cells, which may have the form of very simple elaters. j Fain. 3. Marchantiece Air-chambers (with exception of Dumortiera') highly developed, and the chambers in most cases containing a loose filamentous assimilative tissue. Pores upon the dorsal surface always present (except in Dumortiera) and highly developed, ring-shaped or cylindrical. Sexual organs always in groups, usually upon special long-stalked receptacles. Sporogonium stalked and when ripe breaking through the calyptra, opening by teeth or a circular cleft, more seldom by four or eight valves. The archesporium develops sterile cells, usually in the form of elaters, as well as spores. The Marchantiacece The Marchantiaceae constitute a very natural order of plants, all of whose members agree very closely in their fundamental structure. 1 he separation of the Ricciaceae as a group co¬ ordinate with the Jungermanniaceae and Anthoceroteae is not warranted, as more recent investigations, especially those of Leitgeb,1 have shown that the two groups of the Marchantiaceae and Ricciacese merge almost insensibly into each other. They are all of them strictly thallose forms, the thallus being unusually thick and fleshy, and range in size from a few millimetres in some of the smaller species of Riccia, to 10 to 20 centimetres in some of the larger species of Dumortiera and ConocepJialus. In most of them branching is prevailingly dichotomous, and as this is rapidly repeated, it often causes the thallus to assume an orbicular outline. Some forms, however, e.g. Targionia (Fig. 1, E), fork comparatively seldom, and the new branches are for the most part lateral. The thallus is fastened to the substratum by rhizoids, which are unicellular and usually of two kinds, those with smooth walls and those with peculiar papillate thickenings or teeth that project inward (Fig. 11). I he cells of the lower layers of tissue are usually nearly or quite destitute of chloroplasts, which, however, occur Leitgeb (7), vol. iv. 1 II MUSCINEEE — HEP A TICEE — MARCH ANTI A CEsE in large numbers in the so-called chlorophyll-bearing layer, just below the dorsal epidermis. This chlorophyll -bearing layer FiG. i. — Marchantiaceae. A, B, Male plants of Fimbriaria Californica (Hampe). A, from above ; B, from below ; <$ , antheridial receptacle; /, ventral lamellae, X4 ; C, Riccia glauca (L.), X6; s/>, sporogonia; D, Conocepkalus conic us (Corda), X4; E, Tcirgionia hypophylla (L.)5 X2 ; <$ , antheridial branch. contains air-spaces in all forms except some species of Dumortiera , and these spaces are either simple narrow canals, 24 MOSSES AND FERNS CHAP. as in Riccia glauca, or they may be large chambers separated by a single layer of cells from their neighbours. Such forms occur In most of the higher Marchantiaceae. The growth of the thallus is due to the division of a small group of cells occupying the bottom of the heart-shaped indent¬ ation in the forward part of the thallus. Sections parallel to the surface, cutting through this group, show a row of marginal cells that appear very much alike, and it is impossible always to tell certainly whether or not there is a single definite initial cell. Such a single initial is unquestionably present in the earlier stages, and it is quite possible that it may persist, but owing to its small size and its close resemblance to the adjoin¬ ing cells, this cannot be positively asserted. In vertical sections the initial cell (or cells) appears nearly triangular, with the free outer wall somewhat convex. From this cell two sets of segments are cut off, the dorsal segments giving rise to the green tissue, and the lower segments producing the ventral lamellae and colourless lower layers of cells of the thallus. The plants multiply asexually either by the older parts of the thallus dying away and leaving the growing points isolated, or lateral branches, which are often produced in great numbers from the lower surface of the midrib, become detached and each branch forms a separate plant. The well-known gemmae of Marchantia and Lunularia are the most striking examples of special asexual reproductive bodies. The sexual organs are always derived from the dorsal segments of the apical cell, either of the ordinary branches or of special shoots. The archegonium is of the regular form, and the antheridium always shows a series of transverse divisions before any longitudinal walls are formed in it. While the gametophyte may reach a very considerable degree of specialisation, the sporophyte is relatively insignificant even in the higher forms, and has the foot and stalk poorly developed. While the Marchantiaceae grow for the most part in moist situations, and some of them, e.g. Marchantia polymorpha, are very quickly killed by drying, some species, e.g. Riccia hirta , a common Californian species, grows by preference in exposed rocky places exposed to the full force of the sun. This latter species as well as several others of the same region, e.g. Fimbriaria Californica , Targionia hypophylla , do not die at the end of the rainy season, but become completely dried up, in II MUSCINEsE — HEP A TICsE — MARCH ANTI A CE.E 25 which condition they remain dormant until the autumn rains begin, when they absorb water and begin to grow again at once. In these cases usually only the ends of the branches remain alive, so that each growing tip becomes the beginning of a new plant. The Ricciacece As a type of the simplest of the Marchantiaceae, we may take the genus Riccia , represented, according to Schiffner,1 by 107 species, distributed over the whole earth. Most of them are small terrestrial plants forming rosettes upon clay soil, or sometimes on drier and more exposed places. A few species, e.g. R. fluitans , are in their sterile condition submersed aquatics, but only fruit when by the evaporation of the water they come in contact with the mud at the bottom. p G 2_ _ Riccia. glauca (L.). Development of the archegonium, X525. A, Vertical section through the growing point ; jr, apical cell ; ar, young archegonium; ll, ventral lamella;; B-F, successive stages in the development of the archegonium, seen ill longitudinal section ; G, cross-section of young archegonium (diagrammatic). The dichotomously branched thallus shows a thickened midrib, which is traversed upon the dorsal surface by a longi¬ tudinal furrow which in front becomes very deep. At the bottom of this furrow, at the apex of the thallus, lies the growing point. A vertical section through this shows a nearly triangular 1 Schiffner (1), p. 14. 26 CHAP. MOSSES AND FERNS apical cell which lies much nearer the ventral than the dorsal surface (Fig. 2, x). From this are cut off successively dorsal and ventral segments. Each segment next divides into an inner and an outer cell. From the outer cells of the dorsal segments the sexual organs arise, and from those of the ventral segments the overlapping lamellae upon the lower surface of the thallus, and also the root-hairs. The rapid division of the inner cells of the segments, especially those of the dorsal ones, causes the thallus to become rapidly thicker back of the apex. Fig. 3. — Riccia glauca (L.). Horizontal sections of the growing point. A, B, X525 ; C, X about 260. C shows the dichotomy of the growing point ; .r, jr', the two new growing points ; L, the lobe between them ; ar , a young archegonium. Sections made parallel to the surface of the thallus, and pass¬ ing through the growing point (Fig. 3), show that the margin is occupied by a group of cells that look very much alike. Sometimes one of these cells is somewhat larger than the others, but more commonly it is impossible to decide with certainty that a single initial is present. From a comparison of the two sec¬ tions it is at once evident that the initial cells have nearly the form of the segment of a disc, and that in addition to the dorsal and ventral segments lateral ones are cut off as well. In the region just back of the apex the tissue of the thallus is II MUS C1NEJE — HEP A TICJE — MARCH ANTI A CEsE 27 compact, but in the older parts a modification is observable both on the dorsal and ventral surfaces. In the former, a short distance from the growing point, the superficial cells project in a papillate manner above the surface. This causes little depressions or pits to be formed between the adjacent cells (Fig. 3, C). The subsequent divisions in the papillae are all transverse, and this transforms each papillate surface cell into a row of cells which, as it elongates, causes the pits between it and the adjacent ones to become deep but narrow air-channels, so that in the older parts of the thallus the upper portion is composed of closely-set vertical rows of chlorophyll¬ bearing cells separated by narrow clefts opening at the surface. In Riccia glauca, as well as other species, the uppermost cell of each row often enlarges very much, and with its fellows in the other rows constitutes the epidermis. According to Leitgeb’s researches this epidermal cell is formed by the first division in the outer cell of the segment, and either undergoes no further division, or by dividing once by a transverse wall forms a two¬ layered epidermis ( R . Bischoffii). On the ventral side the outer cells of the segments project in much the same way, but they remain in close contact laterally with the neighbouring cells, so that instead of forming isolated rows of cells, transverse plates or lamellae, occupying the median part of the lower surface of the thallus, are formed. These remain but one cell thick, and grow very rapidly, and bend up so as to completely protect the growing point. With the rapid widening of the thallus in the older parts these scales are torn asunder, and the two halves being forced apart constitute the two rows of ventral scales found in the older parts. Later these scales dry up and are often scarcely to be detected except close to the growing point. In the case of Ricciocarpus natans,1 instead of a single scale beino- formed, each cell of the horizontal row, which ordinarily gives rise to a single scale, grows out independently, much as do the dorsal surface cells in the other species, and the result is a horizontal series of narrow scales, each one corresponding to a single cell of the original row. These later are displaced by the subsequent growth of the thallus, and their arrangement in transverse series can only be seen in the younger parts. The very rapid increase in length of the dorsal rows of cells as they recede from the growing point soon causes them to o\ciaich 1 Leitgeb (7), vol. iv. p. 29. MOSSES AND FERNS CHAP. the latter, which thus comes to lie in a deep groove ; indeed not infrequently the end cells of the rows on opposite sides of the groove actually meet, so that the groove becomes a closed tube. R. fluitans 1 and R. crystallina differ in some respects from the other forms. In these, owing to a greater expansion of the tissues of the older parts of the thallus, the air-spaces are very much enlarged. In the former they are almost completely closed above, as the epidermal cells, by repeated vertical divisions, keep pace with the growth of the thallus and form a continuous epidermis, with only a small central pore over each of the large air-chambers. In R. crystallina , however, there is no such secondary growth of the epidermal cells, and in consequence the cavities are completely open above, so that the surface of the thallus presents a series of wide depressions separated by thin lamellae. These two species also show some difference as to the ventral scales. Those in R. fluitans are small and do not become separated into two, and in R. crystallina they are wanting entirely. Most of the Ricciaceae multiply by special adventive shoots that arise from the ventral surface of the midrib. These become detached and form new individuals. According to Fellner2 the rhizoids develop at the apex a young plant in a manner entirely similar to t,hat by which the young plant arises from the germ- tube of the germinating spore. By far the commonest method of branching in most species of Riccia is a true dichotomy. The first indication of this process is a widening of the growing point and a corresponding increase in the number of the marginal cells. The central cells of the marginal group now begin to grow more vigorously than the others and to project as a sort of lobe (Fig. 3, C, L), and this lobe divides the initial cells into two groups lying on either side of it. As soon as this is accomplished each new group of initials continues to grow in the same manner as the original group, and two new growing points are established, each of which develops a separate branch. The growth of the middle lobe is limited, and it remains sunk in the fork between the two new branches. The thallus is attached to the substratum by root-hairs of two kinds. The first are smooth-walled elongated cells, with colourless contents, the others much like those of the higher o 1 Leitgeb (7), vol. iv. p. 11. 2 Fellner (1). II MU SC I NEMt — HE PA TICAl — MARCH ANTI A CErE 29 Marchantiacese. Their walls are undulating, and projecting inward are numerous more or less developed spike-like protu¬ berances. The root-hairs arise from large superficial cells of the ventral part of the midrib. They are readily distinguished from the adjacent cells by their much denser contents, even before they have begun to project. The arrangement of the tissues of the fully -developed thallus is best seen in vertical cross-sections. In R. glauca and allied forms four well-marked tissue zones can be readily recognised in such a section. The lowest consists of a few layers of colourless rather loose parenchyma, from which the root-hairs arise, and to which the ventral lamellae are attached. Above this a more compact, but not very clearly limited region, the midrib. The elongated form of the midrib cells, which contain abundant starch but no chlorophyll, is, of course, not evident in cross-section. Radiating from the midrib are closely-set rows of chlorophyll-bearing cells with the character¬ istic narrow air-spaces between. The median furrow is very conspicuous in such a section, and extends for about half the depth of the thallus. Terminating each row of green cells is the enlarged colourless epidermal cells, often extended into a beak-like appendage. In some species, eg. R. hirta, some of the surface cells grow out into stout thick -walled pointed hairs. The Sexual Organs In Riccia the sexual organs are formed in acropetal suc¬ cession from the younger segments of the initial cells, and continue to form for a long time, so that all stages may be met with upon the same thallus. While both antheridia and archegonia may be found together, in the two species R. glauca and R. hirta , mainly studied by myself, I found that as a rule several of one sort or the other would be formed in succession, and that not infrequently antheridia were quite wanting from plants that had borne numerous archegonia. Both archegonia and antheridia arise from single superficial cells of the younger dorsal segments of the initial cells. In their earliest stages they are much alike, the mother cell of the antheridium being, however, usually somewhat larger than that of the archegonium. The cell enlarges and projects as a papilla above the surface, when it is divided by a transverse wall into an outer cell and MOSSES AND FERNS CHAP. an inner one. The latter divides but a few times and forms the short stalk; the outer cell, which has dense granular contents, develops into the archegonium or antheridium as the case may be. In the former case the divisions follow the order already indicated for the typical Liverwort archegonium. In the outer cell, which continues to enlarge rapidly, a nearly vertical wall is formed (Fig. 2, C), which divides the cell into two very unequal parts. This wall is curved and strikes the periphery of the mother cell at about opposite points (Fig. 2, G, i). A second wall of similar form is next formed in the larger cell (G, 2), one end of which intersects the first wall, and finally a third wall (3) intersecting both of the others is formed. The young archegonium seen in vertical section at this stage (Fig. 2, D) shows a large central cell bounded by two smaller lateral ones ; in cross-section the central one appears triangular. Each of the four cells of which the archegonium rudiment is now composed divides into two. The outer ones each divide by radial walls into equal parts, and the central one divides into an upper smaller cell (cover cell) and a lower larger one (Fig. 3, E). The next divisions are horizontal and divide the young archegonium into two tiers of cells. The lower one forms the venter, and the upper one the neck, and next the cover cell divides into four nearly equal cells by intersecting vertical walls. The archegonium at this stage (Fig. 2, F) is somewhat pear-shaped, being smaller at the bottom than at the top, and the basal cell is still undivided. It now rapidly increases in length by the trans¬ verse division and growth of all its cells, and there is at the same time a marked increase in diameter in the venter, which finally becomes almost globular (Fig. 4). The axial cell of the neck, the neck canal cell, divides, according to Janczewski,1 always into four in R. Btschoffii, and the same seems to be true for R. hirta (Fig. 4, A), and probably is the same in other species. The number of divisions in the outer neck cells is various, but is most active in the lower part, but in the central cell of the venter there is always but a single transverse ‘ division which separates the ventral canal cell from the egg. The four primary cover cells enlarge a good deal as the archegonium approaches maturity, and divide by radial walls usually once, so that the complete number is normally eight — 1 Janczewski (1). M US CINE — HE PA TICAE — MARC HA NTIA CEAE Janczewski gives ten in R. Bischoffii. The basal cell finally divides into a single lower cell which remains undivided, com¬ pletely sunk in the thallus, and an upper cell which divides mto a single layer of cells forming part of the venter, and continuous with the other peripheral cells. The mature archegonium (Fig. 4) has the form of a long-necked flask with a much enlarged base. The canal cells are completely indis¬ tinguishable, their walls having become absorbed and the Fig. 4. — A, Archegonium of Riccia hirta (Aust.), showing the ventral canal cell ( v ), X525 ; B, ripe archegonium of R. glaitca, longitudinal section, X260. contents run together into a granular mass. The nuclei of the neck-canal cells are small and not readily recognisable after the breaking down of the cell walls, but from analogy with the higher forms it is not likely that they completely disappear in the ripe archegonium. The cytoplasm of the central cell contracts to form the naked globular egg. The cytoplasm is filled with granules, and the nucleus, which is of moderate size, shows a distinct nucleolus, but very little chromatin. A special receptive spot was not certainly to be seen. MOSSES AND FERNS CHAP. Almost coincident with the first cell division in the archegonium rudiment there is a rapid growth of the cells immediately surrounding it. These grow up as a sort of ring or ridge about the archegonium, which is thus gradually immersed in a cup-shaped cavity, and the growth of the cells about this keeps pace with the increase in length of the archegonium, so that even when fully grown only the very extremity of the neck projects above the level of the thallus. The whole process is undoubtedly but a modification of the Fig. 5. A-F, Development of the antheridium of R. glauca, seen in longitudinal section ; G, cross- section of a young antheridium of the same ; H, antheridium of R. hirta ; I, sperm cells of R. glartca. figs. E, F, X150; I, x6 00, the others X300. ordinary growth of the dorsal part of the thallus, and the space about the archegonium is the direct equivalent of the ordinary air-spaces. 1 he first division in the primary antheridial cell is the same as in the archegonium, but the later divisions differ much and do not show such absolute uniformity. The first division wall in the upper cell (Fig. 5, B) is always transverse, and this is followed by a second similar wall, but the subsequent divisions show considerable variation even in the same species. After a varying number of transverse walls have been formed, II MU S CINEAE — HEP A TICAE — MA R CHA NTIA CEjE 33 in most cases the next divisions, which are formed only in the middle segments, are vertical, and divide the segments into quadrants of a circle when seen in transverse section. Occasionally a case is met with where the division walls are inclined alternately right and left, and the divisions strongly recall those of the typical Moss antheridium (Fig. 5, D). The separation of the sperm cells is brought about by a series of periclinal walls in a number of the middle segments, by which four central cells in each segment (Fig. 5, G) are separated from as many peripheral cells. These central cells have, as usual in such cases, decidedly denser contents than the peripheral ones. The lower one or two segments and the terminal ones do not take part in the formation of sperm cells, but simply form part of the wall of the antheridium. The central cells now divide with great rapidity, the division walls being formed nearly at right angles to each other, so that the central part of the antheridium becomes filled with a very large number of nearly cubical cells. The divisions are formed with such regularity that the boundaries of the original central cells remain very clearly marked until the antheridium is nearly mature. The basal cell of the antheridium rudiment in R. glauca divides once by a horizontal wall (Fig. 5, B, D) and forms the short stalk of the antheridium, which, however, is almost completely sunk in the thallus. Between this stalk and the central group of cells there are usually two layers of cells, so that the wall of the antheridium is double at the base, while it has but a single layer of cells in the other parts. The uppermost cells are often, although not always, extended into a beak. The spermatozoids do not seem to differ either in their method of development or structure from those of other Flepaticse, but their excessively small size makes it extremely difficult to follow through the details of their development. When ripe the wall cells are much compressed, but are always to be distinguished. Like the archegonia, the antheridia are sunk separately in deep cavities, which are formed in exactly the same way. Unlike the archegonia, however, the antheridium does not nearly reach to the top of the cavity, whose upper walls are in many species very much extended into a tubular neck, which projects above the general level of the thallus, and through which the spermatozoids are discharged. D MOSSES AND FERNS CHAP. 34 The Embryo After fertilisation is effected the egg develops at once a cell-membrane and enlarges until it completely fills the cavity of the venter. The first division wall is more or less inclined to the axis of the archegonium, but approaches usually the horizontal. The lower of the two cells thus formed divides first by a wall at right angles to the first formed, but this is followed in the upper half of the embryo by a similar division, so that the embryo is divided into nearly equal quadrants. In Fig. 6. — A, B, Young embryos of R . glauca in longitudinal section, showing the venter of the arche¬ gonium, X 260; C, transverse section of a similar embryo, X260; D, longitudinal section of the archegonium and enclosed embryo of R. hirta at a later stage, X220; m , the sterile cells of the sporogonium. each of the quadrants a wall meeting both of the others at right angles next appears (Fig. 6, C, III), and the embryo at this stage consists of eight nearly equal cells. The next walls are not exactly alike, but the commonest form is a curved wall (Fig. 6, C) striking two of the others, usually walls II and III, and intersecting the surface of the embryo. This wall divides the octants into two cells, which appear respectively triangular and quadrilateral in section. By the next division the archesporium is separated from the wall of the sporogonium. These walls II M USCINEjE—HEPA T1CJE — MA Ii CHA NT I A CEAE 35 are periclinal, and by them a single layer of outer cells is separated from the central mass of cells which constitutes the archesporium (Fig. 6, B, D). At first the cells of the embryo are much alike, but as it grows the inner cells increase in size and their contents become densely granular, while the outer cells grow only in breadth, and not at all in depth, assuming more and more a tabular form, and for the most part undergo divisions only in a radial direction, so that the walls remain but one cell thick in most places. As the sporogonium increases in diameter the central cells begin to separate and round off. Their walls become partially mucilaginous, and in microtome sections stain strongly with Bismarck-brown or other reagents that stain mucilaginous membranes. With this disintegration of the division walls the cells separate more and more until they lie free within the cavity of the sporogonium. Each of these spore mother cells is a large gobular cell with thin membrane and densely granular contents. The nucleus is not so large as is usually the case in cells of similar character, and, except the nucleolus, stains but slightly with the ordinary nuclear stains. In the fresh state these spore mother cells are absolutely opaque, owing to the great amount of granular matter, largely drops of oil, that they contain. In embedding these in paraffine, however, the oil is dissolved and removed, and microtome sections show the fine granules of the cytoplasm arranged in a net-like pattern, the spaces between probably being occupied by oil in the living cells. Fig- 7, A shows the nucleus of the mother cell under¬ going the first division. The small size of the nuclei, and the small amount of chromation in them, make the study of the details of the nuclear division difficult here, and as there was nothing to indicate any special peculiarities these were not followed out. After the first nuclear division the daughter nuclei divide again, after which the four nuclei arrange themselves at equal distances from each other, the division walls form simultaneously between them, dividing the spore mother cell into the four tetrahedral spores. A section through such a young spore-tetrad is shown in Fig. 7, B, where one of the cells is somewhat shrunken in the process of embedding. The cell walls at this stage are very delicate and of unchanged cellulose ; but as they grow older MOSSES AND FERNS CHAP. the wall soon shows a separation into endospore and exospore. The latter in R. hirta , which was especially studied, is very thick, at first yellowish in colour, but deepening until when ripe it is black. Sections parallel to the surface show in this species what appear to be regular rounded pits, but vertical sections of the spore-coat show that this appearance is due to a peculiar folding of the exospore, which also shows a distinct striation, the outer layer being much thicker and denser than the inner ones. The nucleus of the ripe spore is remarkably A I- ig. 7. Riccia hirta (Aust.). A, Section of a spore mother cell undergoing its first division, x6oo ; B, section of young spore tetrad, X 300 ; C, section of ripe spore, X 300 ; D, surface view of the exo- spore of a similar stage, x 300. small, and it is evident that the dense contents of the ripe spore is largely oil or some similar soluble matter, as in microtome sections there is very little granular matter visible. At the same time that the first division wall forms in the embiyo, the outer cells of the venter begin to divide by periclinal walls, so that the single layer of cells in the wall of the unfertilised archegonium becomes changed into two, and the basal portion becomes still thicker ; the neck takes no part in this later growth. I he cells of the venter develop a great deal of chlorophyll, which is quite absent from the sporogonium itself, and before the spores are ripe the inner layer of cells of II M U SC I NEsE — H EPA TIC MARCH ANTI A CE/E 37 the calyptra (venter) becomes almost entirely absorbed, so that only traces of these cells are visible when the spores are ripe. The wall of the sporogonium also disappears almost completely as the latter matures, but usually in microtome sections traces of this can be made out in the ripe capsule, although the cells are very much compressed and partially disorganised. The contents of these cells, as well as the inner calyptra cells, no doubt are used up to supply the growing spores with nourish¬ ment. Thus, when ripe, the spores practically lie free in the cavity surrounded only by the outer layer of calyptra cells. The neck of the archegonium persists and is made conspicuous by the dark brown colour of the inner walls of the cells. Hitherto the germination of the Ricciacese was only known in R. glauca } The account here given is based upon observations made upon R. hirta — a very common Cali¬ fornian species. It fruits in winter and early spring, and the spores remain dormant during the dry summer months. If the spores are sown in the autumn they germinate within a few days by bursting the massive black exospore, through which the colourless endospore enclosing the spore contents projects in the form of a blunt papilla. This rapidly grows out into a long club-shaped filament (Fig. 8, A), much less in diameter than the spore, and into this the spore contents pass. These now contain albuminous granules and great numbers of oil-globules, and among these chlorophyll bodies, which at first are small and not very numerous. They, however, increase rapidly in size, and divide also, so that before the first cell division takes place the chloroplasts are abundant and conspicuous. The formation of the first root-hair does not take place usually until a number of divisions have been formed in the young thallus. The first root-hair (Fig. 9, R) arises at the base of the germinal tube, and is almost free from granular contents. It, usually at least, is separated by a septum from the germ-tube. The first wall in the latter is usually transverse, although in exceptional cases it is oblique (Fig. 8, B), and this is followed by a second one parallel to the first (Fig. 8, C). In each of these cells a vertical wall is formed, and then a second at right angles to this, so that the nearly globular mass of cells at the end of the germ -tube is composed of eight nearly equal cells or octants. As these divisions proceed the 1 Fellner (1). MOSSES AND FERNS CHAP. oil drops which are so abundant in the undivided germ-tube disappear almost completely, and are doubtless used up by the growing cells. According to Leitgeb’s view, and that of other authors, the eight-celled body at the end of the germ-tube is a sort of protonema, from which the gametophore arises as a lateral outgrowth. I have seen nothing in the species under consider¬ ation which supports such a view. Here the axis of growth is continuous with that of the germ-tube, and in some cases at least, and probably always, a single apical cell is developed A. at the apex at a very early stage. Probably this initial cell is one of the four terminal octant cells resulting from the first divisions. This cell sometimes has but two sets of segments cut off from it at first, alternately right and left, but whether this form is constant in the young plant I cannot now say. The four lower quadrants also divide, at first only by transverse walls, and these cells lengthening give rise to a cylindrical body composed of four rows of cells, terminated by the more actively dividing group of cells at the summit. The single apical cell is soon replaced by the group of initials found in the full-grown gametophyte, and the method of growth from II MU S CINEAL — HEP A TIC&—MA RCHANT1A CE^E 39 now on is essentially the same. The growth of the cells in the forward part of the dorsal surface of the young thallus is more active than that of the ventral side, so that they project over the growing point (Fig. 9), and as the outer cells of the lateral segments of the apical cell (or cells) also increase rapidly in size as they recede from the growing point, the forward margin pIG_ - _ Riccia hirta (Aust.). Later stages of germination. A, from below, X260; B, optical section of A, showing apical cell jc, X 520 ; C, X 85 ; r, root-hairs. of the thallus, seen from below, is deeply indented, and the forward part of the thallus is thus occupied by a deep cavity, at the bottom of which, toward the ventral side, lies the growing point. This cavity is the beginning of the groove or furrow found in the older thallus. At first the cells of the young thallus are without inter¬ cellular spaces, but at an early period (Fig. 9, C) the outer cells 40 MOSSES AND FERNS CHAP. of the young segments separate and form the beginnings of the characteristic air-spaces. In R. hirta some of the dorsal cells about the same time form short pointed papillae, the first indica¬ tion of the pointed hairs characteristic of this species. As the plant grows, new root-hairs are formed by the growing out of ventral cells into papillae, which are cut off by a partition from the mother cell. These first-formed root-hairs are always smooth-walled, and it is only at a much later stage that the other form develops, as well as the ventral lamellae, which are quite absent from the young plant. Classification of the Ricciacece Besides the genus Riccia, which includes all but three species of the family, there are two other genera, each represented by a single species, which undoubtedly belong here. Of these Ricciocarpus natans is of almost world-wide distribution. It is a floating form which, like Riccia fluitans , only fruits when growing upon the earth. Leitgeb 1 has made a very careful study of the structure and development of the thallus, which differs a good deal from that of Riccia , in which genus this plant was formerly placed. The apical growth is essentially the same, and the differentiation of the tissues begins in the same way, but the chlorophyll -bearing tissue is extraordinarily developed. The air-spaces are formed in the same way as in Riccia , but they become very deep, and at an early stage, while still very narrow, are divided by cellular diaphragms into several overlying chambers, which, narrow at first, later become very wide, so that the dorsal part of the thallus is composed of a series of large polyhedral air-chambers arranged in several layers, and separated by walls but one cell thick. The upper chambers communicate with the outside by pores, quite like those of the Marchantieae. The ventral tissue and midrib are rudimentary, and the very long pendent ventral lamellae are produced separately in transverse rows, which however become displaced by the later growth of the thallus, so that their original arrangement can no longer be made out. Oil-bodies like those found in the Marchantieae occur. The fruiting plant, which grows on the margins of ponds, etc. where the floating form is found, is much more richly branched and more vigorous than 1 Leitgeb (7), vol. iv. II M USCINEjE—HEPA TICAL — MARCH ANTI A CEAE 4i the floating form. The ventral scales become shorter, and numerous wide but unthickened root-hairs are formed, which are almost completely lacking in the floating form. The structure of the reproductive organs and sporogonium are essentially the same as in Rtccia, except that the plants are strictly dioecious. The third genus, Tesselina ( Oxymitra ), represented by the single species, T. pyramidata , is much less widely distributed, belonging mainly to Southern Europe, but also found in Paraguay. This interesting form has also been carefully examined by Leitgeb,1 who calls attention to its intermediate position between the Ricciaceae and the Marchantiese. The thallus has all the characters of the latter : air-chambers opening by regular pores, usually surrounded by six guard-cells ; two rows of ventral scales, independent from the beginning ; and the sexual organs united into groups upon special parts of the thallus. The sporogonium, however, is entirely like that of Riccia, so that it may properly be placed in the same family. The plants are dioecious and strictly terrestrial. A third genus, Cronisia , represented also by a single species, C. paradoxa , is placed provisionally with the Ricciaceae by Schiffner,2 but the structure and development have not been investigated with sufficient -completeness to make this certain. It has been found only in Brazil. Schiffner says of this form : “ It belongs perhaps to the Corsinieae, and forms a direct transition from the Ricciaceae to that family.” 1 Leitgeb (7), vol. iv. p. 34. 2 Schiffner (1), p. 15. CHAPTER III MARCH ANTIEHi COMPARING the Marchantieae with the Ricciaceae, the close similarity in the structure and development of the thallus is at once apparent, but the former are more highly developed in all respects. The development of definite air-chambers in the green tissue, and a continuous epidermis with the characteristic pores, is common to all of them with the exception of the peculiar genus Dumortiera , where the development of the air- chambers is partially or completely suppressed. The genera Ricciocarpus and Tessalina on the one hand, and Corsinia and Boschia on the other, connect perfectly Riccia with the higher Marchantiacese as regards the structure of air-spaces and epidermis, as they do in other respects. The epidermal pores in the Marchantiese are sometimes simple pores surrounded by more or less symmetrically arranged guard cells (Fig. I o, D), or they are, especially upon the female receptacles, of a most peculiar cylindrical form, which arises by a series of transverse walls in the primary guard cells (Fig. io, C). There is a good deal of difference in the character of the • air-chambers in different genera. In Reboulia and Fimbriaria , for instance, they resemble a good deal those of Ricciocarpus , or more or less complete division of the primary chambers being produced by the formation of diaphragms or laminae, which give the green tissue an irregular honey-combed appearance, and in these forms there is not a sharp separation of the green tissue from the central colourless tissue. In other genera, Marchantia , Targioma (Fig. 16), Conocephalus, the dorsal part of the thallus is occupied by a single layer of very definite air-chambers, each opening at the surface by a single central pore. Seen from the CHAP. Ill MA RCHA NTIEsE 43 surface the boundaries of these spaces form a definite network which in Conocephalus (Fig. i, D) is especially conspicuous. The bottom of these chambers is sharply defined by the colourless cells that lie below, and the space within the chamber is filled by a mass of short, branching, conferva-like filaments, which in the centre of the chamber have free terminal cells, but toward the sides are attached to the epidermal cells and are more or less confluent with the adjacent filaments. As in Riccia root-hairs of two kinds are present, but the thickenings in the tuberculate rhizoids (Fig. I i) are much more pronounced, and these are not infrequently branched, A. Fig. io. — Fimbriaria Cali/omica (Hampe). Development of the pores upon the archegonial receptacle, X260. A, B, C, in longitudinal section ; D, view from above. and may extend nearly across the cavity of the hair. The ventral scales are not produced by the splitting of a single lamella, as in Riccia , but are separate from the first and usually arranged in two rows. Leitgeb 1 recognises two types of these organs. In their earliest stages they are alike, and both arise from papillae close to the growing point. In both cases this papillae is cut off from a basal cell, but in the first type ( Sauteria , Targionia , Dumortiera :) it remains terminal, usually forming the tip of a leaf-like terminal appendage of the scale. In the second type, represented by most of the other genera, this originally terminal papilla is forced to one side by the development of a lateral appendage to the scale, 1 Leitgeb (7), vol. vi. p. i7- 44 MOSSES AND FERNS CHAP. which, arising at first from a single cell, rapidly increases in size, and forms the overlapping dark purple marginal part of the scale so conspicuous in many species. In different parts of the thallus are found large mucilage cells, which are usually isolated, or in Cono- cephalus , according to Goebel’s 1 investigations, they may form rows of cells which become confluent so as to form mucilage ducts. In the earlier stages these cells have walls not differing from those of the adjacent cells, but as they grow older the whole cell wall is dissolved, and the space occupied by the row of young cells becomes an elongated cavity filled with apparently structureless mucilage. These cells are recognisable at an early period, as their contents are much denser and more finely granular than those of the adjacent cells. Small cells, each con¬ taining a peculiar oil body, are found abundantly in citantia poiy- most species, both in the body of the thallus Part^oT a tuber- and in the ventral scales. The structure and X525. ’ development of these curious bodies, which are found also in many other Hepaticae, have been carefully studied by Pfeffer.2 The oil body has a round or oval form usually, and in the Marchantieae usually is found in a special cell which it nearly fills. It is brown or yellowish in colour, and has a turbid granular appearance. The extremely careful and exhaustive study of these bodies by Pfeffer has shown that the oil exists in the form of an emulsion in water, and that in addition to the oil and water more or less albuminous matter is present, and tannic acid. 1 he latter is especially abundant in the oil bodies of Lunularia, less so im Marchantia and Preissia. The thallus of the Marchantiaceae is made up almost entirely of parenchyma, but Goebel 3 states that in Preissia comniutata there are elongated sclerenchyma-like cells in the midrib. The walls of the large colourless cells of the lower layers of the thallus are often marked with reticulate thickenings, which are especially conspicuous in Marchantia. Most of the Marchantieae have no special non-sexual reproductive organs, but in the genera Marchantia and Lunularia special gemmae are produced in enormous numbers ; 1 Goebel (5), p. 531- 2 Pfeffer (2). 3 Goebel. Ill M A R CH A N TIEsE 45 and in the latter form, which is extremely common in green¬ houses, the plant multiplies only by gemmae, as the plants are apparently all female. 1 hese gemmae, as is well known, are produced in special receptacles upon the dorsal side of the thallus. The receptacles are cup-shaped in Marchantia , and crescent-shaped in Lunularia , where the forward part of the margin of the cup is absent. These cups are apparently Fig. 12. — Marchantia polymorpha (L.). A, Plant with gemma cups (h, k ), X2 ; JB-F, develop¬ ment of the gemmae, X 525 ; G, an older gemma, X 260 ; v , z/, the two growing points. specially developed air-chambers, which, closed at first, except for the central pore, finally become completely open. The edge of the fully-developed receptacle is fringed. The gemmae arise from the bottom of the receptacle as papillate hairs, and their development is the same in the two genera where they occur. Fig. 1 2 shows their development in M. polymorpha. One of the surface cells of the bottom of the receptacle projects as a papilla above the surface, and is cut off by a transverse wall from the cell below. The outer cell next 46 MOSSES AND FERNS CHAP. divides again by a transverse wall into a lower cell, which develops no further, and a terminal cell from which the gemma is formed. This terminal cell first divides into two equal cells by a cross-wall (Fig. I 2, B), and in each of these cells a similar wall arises, so that the young gemma consists of four nearly equal superimposed cells (Fig. 1 2, D). The wall III in Fig. 12, D, arises a little later than wall II, and is always more or less decidedly concave upward. Each of the four primary cells of the gemma is divided into two by a central vertical wall, and this is followed by periclinal walls in each of the resulting cells. At first the gemma is but one cell in thickness, but later walls are formed in the central cells parallel to the surface, so that it becomes lenticular. As it grows older there is established on opposite sides (Fig. 12, G, v, v') two growing points, which soon begin to develop in the manner found in the older thallus, and come to lie in a depression, so that the older gemmae are fiddle-shaped. The gemma stands vertically, and there is no distinction of dorsal and ventral surfaces. The cells contain chlorophyll, except here and there the cells with oil bodies, and an occasional large colourless superficial cell. Among them are small club-shaped hairs, which secrete a mucilage that swells up when wet, and finally tears away the gemmae from their single-celled pedicels. The further development of the gemmae depends upon their position as to the light. Whichever side happens to fall down¬ ward becomes the ventral surface of the young plant, and the colourless cells upon this surface grow out into the first rhizoids. The two growing points persist, and the young plant has two branches from the first, growing in exactly opposite directions. As soon as it becomes fastened to the ground the dorsiventrality is established, and upon the dorsal surface the special green lacunar tissue and the epidermis with its characteristic pores are soon developed, while the ventral tissue loses its chlorophyll, and soon assumes all the characters found in the mature thallus. The branching of the thallus is in most cases dichotomous, as in Riccia , but occasionally, as in Targionia (Fig. i, E), the growth is largely due to the formation of lateral adventitious branches produced from the ventral surface. In structure and development the sexual organs correspond closely to those of the Ricciaceae, but they are always formed Ill MA R CHA N TIE AC 47 in more or less distinct groups or “ inflorescences.” As might be expected, this is least marked in the lower forms, especially the Corsinieae,1 where the main distinction between them and the lower Ricciaceae is that in Corsinia the formation of sexual organs is confined to a special region, and that the archegonia do not have an individual envelope as in Riccia, but the whole group of archegonia is sunk in a common cavity, which is of exactly the same nature as that in which each archegonium is placed in the latter. In most of the Marchantieae, however, both antheridia and archegonia are borne in special receptacles, which in the case of the latter are for the most part specially modified branches or systems of branches, raised at maturity upon long stalks (Fig. 1 9). The antheridial receptacles are sometimes stalked, but more commonly are sessile, and often differ but little from those of the higher Ricciaceae. The sporogonium shows an advance upon that of the Ricciaceae by the development of a lower sterile portion, or foot, in addition to the spore-bearing portion or capsule, and in the latter there are always sterile cells, which in all but the lowest Corsinieae have the form of elaters. At maturity, also, the ripe capsule breaks through the calyptra, except in the Corsinieae, where, too, the sterile cells do not develop into elaters, but seem to serve simply as nourishing cells for the growing spores. The stalk of the capsule is always short compared with that of most Jungermanniaceae, and the wall of the capsule remains intact until the spores are ripe. The spores vary much in size, and in the development of the outer wall. In Marchantia polymorpha and other species where the spores germinate promptly, the ripe spore contains chlorophyll, and the exospore is thin and slightly developed. In such cases there is no distinct rupture of the exospore, but the whole spore elongates directly into the germ -tube. In Conocephalus, where the spores are very large, the first divisions occur in the spores before they are scattered. In species where the spores do not germinate at once the process is much like that of Riccia , and the thick exospore is ruptured and remains attached to the base of the germ-tube. The apical growth of the Marchantieae is very much like that of Riccia. In Fimbriaria Calif omica (Fig. 13) the apical cells seen in vertical section show the same form as those of 1 Leitgeb (7), vol. iv. 48 MOSSES AND FERNS CHAP. Riccia, and the succession of dorsal and ventral segments is the same ; but here the development of the ventral segments is much greater, and there is not the formation of the median ventral lamellae as in Riccia , but the two rows of ventral scales arise independently on either side of the midrib, very near the growing point, and closely overlap and completely protect the apex. The formation of the lacunae in the dorsal part of the thallus begins earlier than in Riccia , and corresponds very closely to what ob- A. tains in Ricciocarpus. The pits are at first very narrow, but widen rapidly as they recede from the apex. In the epidermal cells sur¬ rounding the opening of the cavity, there are rapid divisions, so that the open¬ ing remains small and forms the simple pore found in this species. As in Riccio¬ carpus , the original air- chambers become divided by the development of partial diaphragms into sec¬ ondary chambers, which are not, however, arranged in any regular order, and com¬ municate more or less with Fig. 13. — Fimbriaria. Californica (Hampe). A, Ver- Qne another tical section through the apex of a sterile shoot, show¬ ing the formation of the air-chambers ; jr, the apical cell, X300 ; B, similar section through an older part of the thallus, cutting through a pore, X 100. In Targionia (Figs. 16, 1 7), where the archegonia are borne upon the ordi¬ nary shoots, the growth of the dorsal segments is so much greater than that of the ventral ones that the upper part of the thallus projects far beyond the growing point, which is pushed under toward the ventral side. A similar condition is found in the archegonial receptacles of other forms, where this includes the growing point of the shoot (Fig. 1 9). In Targionia the lacunae are formed much as in Fimbriaria , but they are shallower and much wider, and the pores corre¬ spondingly few. 1 he assimilative tissue here resembles that Ill MARCHANTIEJE 49 of Marchantia and others of the higher forms. It is sharply separated from the compact colourless tissue lying below it, and the cells form short confervoid filaments more or less branched and anastomosing, and except in the central part of the chamber united with the epidermal cells. Under the pore, however, the ends are free and enlarged with less chlorophyll than is found in the other cells. All of the Marchantieae except the aberrant genus Dumor- tiera correspond closely to one or the other of the above types in the structure of the thallus, but in the latter the air- chambers are either rudimentary or completely absent, and the ventral scales are also wanting. Leitgeb 1 investigated D. irrigua , whose thallus is characterised by a peculiar areolation composed of projecting cell plates, and came to the conclusion that these were the remains of the walls of the air-chambers, whose upper parts, with the epidermis, were thrown off while still very young. He had only herbarium material to work < with, but in this he detected traces of the epidermis and pores in the younger parts. I examined with some care fresh material of D. trichocephala, from the Hawaiian Islands, and find that in this species, which has a perfectly smooth thallus without areolations, that no trace of air-chambers can be detected at any time. Vertical sections through the apex show the initial cells to be like those of other Marchantiaceae, and the succession of segments the same, but no indications of lacunae can be seen either near the apex or farther back, the whole thallus being composed of a perfectly continuous tissue without any intercellular spaces, and no distinct limit between the chlorophyll -bearing and the colourless tissue. As Dumortiera corresponds in its fructification with the higher Marchantieae, the peculiarities of the thallus are probably to be regarded as secondary characters, perhaps produced from the environment of the plant, and species like D. irrigua would form transitional stages between the typical Marchantiaceous thallus and the other extreme found in D. trichocephala. The structure and development of the sexual organs are very uniform among the Marchantieae. In Fimbriaria Cali¬ fornia, which is dioecious, the antheridial receptacle forms a thickened oval disc just back of the apex. Not infrequently (Fig. i, A), when the formation of antheridia begins not long 1 Leitgeb (7), vol. vi. p. 124. E 5° MOSSES AND FERNS CHAP. before the forking of the thallus, both of the new -growing points continue to develop antheridia for a time, and the receptacle has two branches in front corresponding to these. The receptacle is covered with conspicuous papillae which mark the cavities in which the antheridia are situated. Verti¬ cal longitudinal sections through the young receptacle show antheridia in all stages of development, as their formation, like those of Riccia, is strictly acropetal. The first stages are exactly like those of Riccia , and the primary cell divides into two cells, a pedicel and the antheridium proper. The divisions in the lower cell are somewhat irregular, but more numerous than in Riccia , so that the stalk of the ripe anther¬ idium is more massive (Fig. 14). In the upper cell a series Fig. 14 .—Fimbriaria sfi. (?). A, Part of a vertical section of a young antheridial receptacle, showing two very young antheridia ( (}), X420 ; B-E, older stages. of transverse walls is formed, varying in different species in number, but more than in Riccia , and apparently always perfectly horizontal. In Marchantia polymorpha Strasburger 1 found as a rule but three cells, before the first vertical walls were formed. In an undetermined species of Fimbriaria (hig. 14)1 much like F. Calif "ormca, the antheridia were un¬ usually slender, and here frequently four, and sometimes five transverse divisions are formed before the first vertical walls appear. Sometimes all the cells divide into equal quadrants bv intersecting vertical walls, but quite as often this division does not take place in the uppermost and lowest cell of the body of the antheridium, or the divisions in these parts are more Strasburger (2). Ill MA RCHA NTIEsE 5i irregular. The separation of the central cells from the wall is exactly as in Riccia, and the lower segments do not take any part in the formation of the sperm cells, but remain as the basal part of the wall. In Fimbriaria the top of the antheridium is prolonged as in Riccia, but in Marchantia this is not the case. The wall cells, as the antheridium approaches maturity, are often much compressed, but in Targionia hypophylla , Fig. 15. — Fimbriaria Calijornica (Hampe). A, Longitudinal section of a fully-developed male re¬ ceptacle, x8 ; B, longitudinal section of a nearly ripe antheridium, X 100 ; C, young sperm cells, X600; D, spermatozoids, X1200. where Leitgeb 1 states that this compression is so great that the cells appear like a simple membrane, I found that, so far from this being the case, the cells were extraordinarily large and distinct, and filled the whole space between the body of the antheridium and the wall of the cavity, which in Leitgeb’s figures 2 is represented as empty. The antheridium becomes sunk in the thallus precisely as in Riccia. The sperm cells are nearly cubical and the spermatozoid is formed in the 1 Leitgeb (7), vol. vi. PI. X. Fig. 12. 2 Leitgeb, l.c. 52 MOSSES AND FERNS CHAP. usual way. The free spermatozoid (Fig. 15, D) shows about one and a half complete turns of a spiral. The cilia are very long, and the vesicle usually plainly evident. When the antheridia are borne directly upon the thallus, the apical growth continues after antheridia cease to be formed, and the receptacle is thus left far back of the growing-in point. In forms like Targionia , however, where there are special antheridial branches, the growth of these is limited, and gener¬ ally ceases with the formation of the last antheridia. The most specialised forms are found in the genus Marchantia and its allies, where the antheridial receptacle is borne upon a long stalk, which is a continuation of the branch from which it grows, and the receptacle is a branch-system. The growing point of the young antheridial branch forks while still very young, and this is repeated in quick succession, so that there results a round disc with a scalloped margin, each indentation marking a growing point, and the whole structure being equivalent to such a branch system as is found in Riccia or Anthoceros, where the whole thallus has a similar rosette - like form. The antheridia are arranged in radiating rows, the youngest one nearest the margin and the eldest in the centre. In some tropical species, eg. M. geminata , the branches of the receptacle are extended and its compound character is evident. The archegonia are never sunk in separate cavities, but stand free above the surface of the thallus. The simplest form may be represented by Targionia. Here the archegonia arise in acropetal succession from the dorsal segments of the initial cells of the ordinary branches. A superficial cell enlarges and is divided as in Riccia into an outer and an inner cell. The latter undergoes irregular divisions and its limits are soon lost. In the outer cell the divisions occur in the same order as in Riccia , but from the first the base of the archegonium is broad and not tapering. Strasburger1 states that in Marchantia there is a division of the outer of the two primary cells by a wall parallel to the first, and that the lower one forms the foot of the archegonium, and Janczewski 2 gives the same account of the young archegonium of Preissia commutata. This certainly does not occur in Targionia, and to judge from the later stages of Finibnana Calif ornica , this species too lacks Strasburger (2), p. 416. 2 Janczewski (1), p. 386. Ill MARC HA NTIEsE 53 thib division. The full-grown archegonium is of more nearly uniform thickness than in Riccia , as the venter does not become so much enlarged. The neck canal cells are more numerous, about eight being the common number, but in Targionia the lormation of division walls between these is sometimes sup- A Fig. i 6. — Targionia hypophylla (L.). A, Longitudinal section of the thallus, x ioo ; ar , archegonia ; //, ventral scales ; B, median section through a pore, showing the assimilating cells (cl) below, X300. pressed (Fig. 17, C), so that this may account for Janczewski’s1 error in stating that the number was always four, as the nuclei in unstained sections might be very easily overlooked. The cover cells are somewhat smaller than in Riccia and do not usually undergo as many divisions, there being seldom more 1 Janczewski (i), p. 386. 54 MOSSES AND FERNS CHAP. than six in all. In Targionia (Fig. 21, A), and Strasburger observed the same in Marchantia , the ripe egg shows a distinct “ receptive spot,” that is, the upper part of the unfertilised egg is comparatively free from granular cytoplasm, while the lower part, about two-thirds in Targionia , is much more densely granular. The nucleus is not very large and has very little chromatin. The nucleolus is large and distinct and stains very intensely. As the archegonium of Targionia matures, its neck elongates rapidly and bends forward and upward, no Fig. 17. — Targionia hypopJiylla (L.). A, Longitudinal section of the apex of the thallus, with young archegonia ( ar ), X525; x, the apical cell; B, young; C, older archegonium in longitudinal section ; D, cross-section of the archegonium neck, X525. doubt an adaptation to facilitate the entrance of the sper- matozoid. A similar curving of the archegonium neck is observed in other forms where the archegonium is upon the lower side of the receptacle. After an archegonium (or sometimes several of nearly equal age) is fertilised, the growth in length of the thallus stops, but there is a rapid lateral growth with results in the formation of two valves, which meet in front much like the two parts of a bivalve shell, and this involucre completely encloses the young growing sporogonium. 1 Strasburger (2), p. 418. Ill MARCHANTIEJE 55 In the simplest cases, where the archegonia are borne upon a receptacle 1 which is raised upon a stalk, eg. Plagiochasma, Clevea (Fig. iS, A), the receptacle does not represent, according to Leitgeb,2 a complete branch, but is only a dorsal outgrowth of the latter, which may grow out beyond it, or even form several receptacles in succession. The first indication of the receptacle is a dor- A. 9. B. sal prominence which soon becomes almost hemispherical, and near the hinder margin the first archegonium arises, without, appar¬ ently, any special re¬ lation to the growing point. On the lat¬ eral margins are then formed two other arche¬ gonia, not, however, simultaneously ; and finally a fourth may be formed in front : three or four archegonia in all seem to be the ordinary number. The stalk of the receptacle is also a dorsal append¬ age of the thallus, and not a direct continua¬ tion of it. The next type is that which Leitgeb " attributes to Fimbriaria , and some others, but it in Fimbriaria Californica. In this 9. Fig. i 8. — A. Clevea sp. A, longitudinal section of the thallus showing the dorsal origin of the female receptacle ( 9 ) ; v, the growing point (diagram after Leitgeb) ; B, Reboulia hemispharica (Radd.), longitudinal section of very young receptacle with the first archegonium ( $ ) ; ur, the apical cell, X 300 (after Leitgeb). Grimaldia , Reboulia , is not the type found type the structure of the receptacle and the origin of the archegonia are the same as in that just described; but here the growing point of the branch forms the forward margin of the receptacle, and the stalk is a direct continuation of the axis of the 1 The sporogonial receptacle of the Marchantieae is sometimes known as the C“S°S“m7), vol. vi. 29. • Leitgeb, p 30. s6 MOSSES AND FERNS chap. branch. Upon its ventral surface it shows a furrow in which root -hairs are produced in great numbers, and this furrow F ig. 19. — Fimbriaria Calif omica (Hampe). A, Plant with two fully-grown sporogonial receptacles, natural size ; B, a single receptacle, X4 ; C, the same cut longitudinally, showing the sporogonium (sp), enclosed in the perianth (per) ; D, nearly median section of a young receptacle showing one growing point (_r) and an archegonium (ar) ; L, air-spaces; sty a pore; r , rhizoids, X40 ; E, the growing point of the same with an archegonium, x 300 ; x, the apical cell. passes over into the ventral surface of the thallus (Fig. 19, B). Ill M ARCHA NTIEAh 57 The highest type is that of Leitgeb’s 1 “ Compositse.” Here the female receptacle is a branch system similar to that of the male receptacle of Marchantia. The branching is usually completed at a very early period, while the receptacle is almost concealed in the furrow in the front of the thallus. A simple case of this kind is seen in Fimbriaria Californica (Fig. 1 9). Here there are four growing points that have arisen from the repeated dichotomy of the primary growing point of the branch, and each of these gives rise to archegonia in acropetal succession, much as in Targionia , but the number of archegonia is small, not more than two or three being as a rule formed from each apex. The development of the dorsal tissue is excessive and the ventral growth reduced to almost nothing, and the growing apices are forced under and upward and lie close to the stalk, and the archegonia have the appearance of being formed on the ventral side of the shoot, although morphologically they are dorsal structures. In the common Marchantia polymorpha the branched character of the receptacle is emphasised by the development of the “ middle lobe ” between the branches. These lobes grow out into long cylindrical appendages between the groups of archegonia, and give the receptacle a stellate form. Usually in M. polymo7'pha there are eight growing points in the receptacle, and of course as many groups of archegonia, which are much more numerous than in any other genus, amounting to a hundred or more in one receptacle. In Marchatitia , as well as some other genera with compound receptacles, there are two channels in the stalk, showing that this is here influenced by the first dichotomy. While the archegonia, before fertilisation, are quite free, the whole group of archegonia, and indeed the whole receptacle, is invested with hairs or scales of various forms that originate either from the epidermis of the dorsal side, or as modifications of the ventral scales. The lacunar tissue is very much developed upon the receptacles, as are to an especial degree the peculiar cylindrical breathing pores. The formation of these begins in the same way as the simple ones, being merely the original opening to the air-space. This seen from the surface shows an opening with usually five or six cells surrounding it. Vertical sections show that very soon the cells surrounding the pore become 1 Leitgeb (7), vol. vi. p. 33. 58 MOSSES AND FERNS CHAP. deeper than their neighbours and project both above and below them. In these cells next arise (Fig. io, A, B) a series of inclined walls by which each of the original cells is transformed into a row of several cells, and these rows together form a curious barrel-shaped body surrounding the pore. The upper cells converge and almost close the space above, and this is still further diminished by the cuticle of the outer cell wall of the uppermost cells growing beyond the cells and leaving simply a very small central opening. The rows of cells also converge below, and in Fimbriaria Californica the lowermost cells are very much enlarged, and probably serve to close the cavity completely at times, and act very much like the guard cell of the stomata of vascular plants. In Leitgeb’s group of the Astroporae, the simple pores of the thallus have the radial walls of the surrounding cells strongly thickened, so that the pores seen from the surface appear star-shaped. The most specialised of the Marchantiece , i.e. Marchantia , Lunularia , etc., have the cylindrical pores upon the vegetative part of the thallus as well as upon the receptacle, but in the others they occur only upon the latter. The Sporogonium The first divisions in the embryo of the Marchantiece are the same as in the Ricciaceae, but only the upper part (capsule) of the sporogonium develops spores, while the rest becomes the stalk. The simplest form of capsule is found in the genera Corsima and Boschia, which have been carefully studied by Leitgeb.1 In these the embryo, instead of remaining globular as it does in Riccia , elongates and very early becomes differenti¬ ated into a nearly globular upper part, or capsule, and a usually narrower basal portion, the stalk (Fig. 20). In the capsule at a very early period a single distinct layer of outer cells is separated from the central group of cells, and forms the wall of the capsule, which in Boschia at maturity develops upon the inner cell walls thickened bars. Only a portion of the cells of the central part produce spores ; the remainder do not divide after the spore mother cells are formed, but remain either as simple slightly elongated nourishing cells ( Corsinia ) or elaters {Boschia). 1 Leitgeb (7), vol. iv. pp. 45-47. Ill MA RCHA NTIEAZ 59 The other Marchantieae are much alike, and as Tai'gionia was found to be an especially satisfactory form for study, on account of the readiness with which straight sections of the embryo could be made, it was taken as a type of the higher Marchantieae. The first division wall (basal wall) is trans¬ verse, and divides the embryo into two nearly equal parts. This is followed in both halves by nearly vertical walls (quadrant walls), and these and the basal wall are then bisected by the octant walls, so that as in Riccia the young embryo is formed of eight nearly equal cells. In Targionia , even at this period, the embryo is always somewhat elongated instead of globular. The next division walls vary a good deal in different individuals. Fig. 2 1, C shows a very regular arrangement of cells, where the first divisions were much the same in all the quadrants. Here all the secondary walls were nearly parallel with the basal wall, and intersected the quadrant and octant walls ; but quite as often, especially in the upper half of the embryo, these secondary walls may intersect the basal wall. In no cases seen was there any indication of a two-sided apical cell such as Hofmeister1 figures for Targi¬ onia and probably his error arose from Fig. 2o.— Coninia mardmntioids a study of forms where the Quadrant optical section, x3oo(Leitgeb). walls were somewhat inclined, in which case the intersection of one of the secondary walls with it might cause the apex of the embryo to be occupied by a cell that, in section, would appear like the two-sided apical cell of the Moss embryo. The regular formation of octants was observed by me in Fmib'naria Califovnica , and by Kienitz-Gerloff- and others in JVLarchantia^ Gnmaldia , and Preissia, and probably occurs normally in all Mar- chantiacese. After the first anticlinal walls are formed in the octants, no definite order could be observed in the succeeding cell di\isions, 1 Hofmeister (i), PL XV. Figs. 24, 25. 2 Kienitz-Gerloff ( 1, 2). 6o MOSSES AND FERNS CHAP. especially in the lower half of the embryo. In the upper part periclinal walls appear, but not at any stated time, so far as could be made out, and the first ones do not, as Leitgeb asserts, Fig. 21. — Targionia hyfiophylla (L.). A, Longitudinal section of the vepter of a ripe archegonium, X500; B-E, development of the embryo, seen in longitudinal median section — B, two-celled, D, four-celled stages, X 500, except E, which is magnified 150 times ; F, nearly median section of the upper part of an older embryo, X 250. necessarily determine the separation of the archesporium, as in the Corsinieae. The growth now becomes unequal, the cells in the central zone not dividing so actively, a marked constriction Ill MARCHANTIE^E 6i is formed, and the young sporogonium becomes dumb-bell shaped. By this time a pretty definite layer of cells (Fig. 21, F) is evident upon the outside of the capsule, but the cells of the globular lower part, or foot, are nearly or quite uniform. They are larger than those of the capsule, and more transparent. In the latter the wall becomes later more definite, and remains but one cell thick until maturity. The arrange¬ ment of the cells of the archesporium is very irregular, and until the full number of these is formed they are all much alike. Fig. 22. — Targionia hypophylla. (L.). A, Median longitudinal section of older embryo enclosed in the calyptra (cat), X80; B, a portion of the upper part of the same embryo, X4S0; the nucleated cells represent the archesporium ; C, part of the archesporium of a still later stage ; el, elaters ; sp, sporogenous cells, X 480. Just before they separate, however, careful observation shows that two well-marked sorts of cells are present, but intermingled in a perfectly irregular way. A part of these cells are nearly isodiametric, the others slightly elongated, and the nuclei of the former cells are larger and more definite than those of the latter. At this stage the cells begin to separate by a partial deliquescence of their cell walls, and when stained with Bismarck-brown these mucilaginous walls colour very deeply, and the cells are very distinct in sections so treated. They finally separate completely, and the much -enlarged globular 62 MOSSES AND FERNS CHAP. capsule now contains a mass of isolated cells of two kinds, globular sporogenous cells and elongated elaters. The former now divide into four spores, but before the nucleus divides the division of the spores is indicated by ridges which project inward and divide the cavity of the mother cell almost com¬ pletely. With the first divisions in the embryo the venter of the archegonium, which before was only one cell thick, divides by a series of periclinal walls into two layers of cells, which later undergo further divisions, so that the calyptra surrounding the IMG. 23. Fimbnarict Califomica (Hampe). A, Young, B, older embryo in median section. A, X 300 , B, x 100 ; C, upper part of a sporogoniunt, after the differentiation of the archesporium, X 200. older capsule may consist of four or more layers of cells. The neck of the archegonium remains unchanged, but the tissue of the thallus below the archegonium grows actively, and surrounds the globular foot, which has grown down into the thallus for some distance, and only the capsule remains within the calyptra. This large growth of the foot is at the expense of the surrounding cells of the thallus, which are destroyed by its growth, and through the foot nourishment is conveyed from the thallus to the developing capsule. 1 hat is, the sporogonium is here a strictly parasitic organism, growing entirely at the expense of the thallus. Ill MARCHANTIEjE 63 The further growth of the spores and elaters was studied in Fimbnaria Calif ormca. The spores remain together in tetrads, until nearly ripe. In sections parallel to the surface of the younger spores (Fig. 24, C) the outer surface of the exospore is covered with very irregular sinuous thickenings, at first projecting but little above the surface, but afterward becoming m this species extraordinarily developed. In sections of the ripe spore (Fig. 24, D) three distinct layers are evident, the cellulose endospore, the thick exospore, and this outer thickened Fig. 24. — Fbnbriaria Califomica (Hampe). A, Young elater x6oo; B, a fully-grown elater, X 300 ; C, surface view of the wall of a young spore, showing the developing episporic ridges, X600 ; D, section of the wall of a ripe spore, X300. mass of projecting ridges which has every appearance of being deposited from without, and must therefore be characterised as epispore (perinium) ; Leitgeb 1 distinctly states that thickenings of this character do not occur in the Marchantieae, but that the thickenings are always of the character of those in Riccia. The elaters are at first elongated thin-wralled cells with a distinct although small nucleus, and nearly uniformly granular cytoplasm. As they grow the cytoplasm loses this uniform appearance, and a careful examination, especially of sections, shows that the granular part of the cytoplasm begins to form 1 Leitgeb (7), vol. vi. p. 45. 64 MOSSES AND FERNS CHAP. a spiral band, recalling somewhat the chlorophyll band of Spirogyra. This is the beginning of the characteristic spiral thickening of the cell wall, and while at first irregular, the arrangement of the granular matter becomes more definite, and following the line of this spiral band of granules in the cytoplasm, there is formed upon the inner surface of the wall the regular spiral band of the complete elater. This band, which is nearly colourless at first, becomes yellow in the mature elater, and in Targionia , where there are generally two, they are almost black. Not infrequently branched elaters are found, but these are unicellular, and no doubt owe their peculiar form to their position between the spore mother cells in the young archesporium. An axial row of granules, which seem to be of albuminous nature, remains in the elaters of Fimbriaria until maturity. The differences in the structure of the sporogonium in different genera of the Marchantieas are slight. In Marchantia polymorpha , the young sporogonium is nearly globular, and even when full grown it is ellipsoid with the stalk and foot quite rudimentary. Most forms, however, have the foot large, but the stalk, compared with that of most Jungermanniaceas, is short. In most of them the whole of the upper half of the young embryo develops into the capsule, but in Fimbriaria Californica I found that the archesporium was smaller than in other forms described, and that sometimes the apical part of the sporogonium was occupied by a sort of cap of sterile cells (Fig- 23). The dehiscence of the capsule is either irregular, eg. Targionia , or by a sort of lid, eg. Grimaldia, or by a number of teeth or lobes, eg. Lunularia , Marchantia. In some forms after fertilisation there grows up about the archegonium a cup¬ shaped envelope, “ perianth, pseudoperianth,” which in Fimbriaria especially is very much developed, and projects far beyond the ripe capsule (Fig. 19). The germination of the spores corresponds in the main with that of Riccia. Except in cases where the exospore is very thin, in which case it is not ruptured regularly, the exospore either splits along the line of the three converging ridges upon the ventral surface, and through this split the endospore protrudes in the form of a papilla, as in Riccia ; or in Targionia (Fig. 25) the exospore is usually ruptured in two places on Ill MARCHANTIEAE 65 opposite sides of the spore, and through each of these a filament protrudes, one thicker and containing chlorophyll, the other more slender and nearly colourless. The first is the germ tube, Fig. 25.— Targionia hypophylla (L.). Germination of the spores, X about 200. In B two germ tubes have been formed ; C and E are optical sections ; jt, apical cell; r, primary rhizoid ; sp, spore membrane. the second the first rhizoid. In Fimbriaria Calif ornica the first root-hair does not usually form until a later period. In Targionia a curious modification of the ordinary process is quite often met with (Fig. 25, B). Here, by a vertical division in the very young germ tube, it is divided into two similar cells, which both grow out into germ tubes. Whether both of these ever produce perfect plants was not determined, but the first divisions in both were per¬ fectly normal. The first divisions in the germ tube are not quite so uniform as in Rirria hirta but Y'G- *b-—Targimia hyP°Phyiia. ( L.). Germ so umtorm as in jxiccia /in la, dui plant in which the thaljus ^ has been resemble them very closely in the formed secondarily, X260. commoner forms. In Fimbriaria especially, and this has also been observed in F B Fig. 27. — Fimbrictria Cctlifomica (Hampe). A, B, Young plants in optical section, showing the single two-sided apical cell (x), X 260 ; C, horizontal section of an older plant with a single four- sided initial (jit), X425 ; D, E, two young plants, D from below, E from the side, X85. CHAP. Ill MARC HA NTIEAi 6 7 Marchantia 1 and other genera, a distinct two-sided apical cell is usually developed at an early period, and for a time the growth of the young plant is due to the segmentation of this single cell. Finally this is replaced by a single four-sided cell (Fig. 27, C), very much like the initial cell of the mature thallus. The young plant, composed at first of homogeneous chlorophyll - bearing cells, grows rapidly and develops the characteristic tissues of the older thallus. The first rhizoids are always of the simple form, and the papillate ones only arise later, as do the ventral scales. Targionia shows a number of peculiarities, being much less uniform in its development than Fimbriaria. While it often forms the characteristic germ tube, and the divisions there are the same as in Riccia and Fimbriaria , the formation of a germ tube may be completely suppressed, and the first result of germination is often a cell mass, from which later a secondary germ tube may be formed with the young plant at the apex (Fig. 26). Such cases as these are the only ones where it seems really proper to speak of the plant arising secondarily from a protonema, for in other cases, as in Riccia, the growth is perfectly continuous, and the axis of the young thallus is coincident with that of the germ tube, and in no cases observed by me could it in any sense be looked upon as a secondary lateral growth. Classification of the Marchantiece The higher Marchantieae are readily separable into three families, the Corsinieae, Targionieae, and the true Marchantieae. Leitgeb has made a further division of the latter family, but some of the characters given are not sufficiently constant to warrant his division, and for that reason it has been thought best not to accept them.1 2 Thus Fimbriaria Californica, which is, in regard to its fructification, typical, has the female recep¬ tacle of the composite type, a character which, according to Leitgeb, not only does not belong to the genus Fimbriaria , but is not found in any genus of the group (Operculatae) to which he assigns it. This species too does not have the capsule operculate, but opens irregularly. The Corsinieae, as we have 1 Leitgeb (7), vol. vi. PI. IX. Fig. 13. 2 Leitgeb (7) and Schiffner (1), p. 24. 68 MOSSES AND FERNS CHAP. already seen, are exactly intermediate in character between the highest Ricciaceae, such as Tessalina, and the lower Marchantieae, and this is true both of the structure of the thallus and the sporogonium. Corsinia differs from all the higher Marchantieae in the character of the ventral scales, which are formed in more than two rows, like those of Ricciocarpics. Boschia, the other genus, has two rows of scales of the ordinary form. The archegonia are borne in a group in a depression upon the dorsal surface of the thallus, but are not formed upon a special receptacle, although after fertilisation the cells at the bottom of the cavity multiply actively and form a small prominence upon which the young sporogonia are raised, and this may perhaps be the first indication of the archegonial receptacle in the other forms. The Targioniece include the two genera Targionia, which has been already described at length, and Cyathodium } a genus whose development is not sufficiently known to make its systematic position quite certain. In the position of the sexual organs, and the formation of the two-valved involucre about the fruit, as well as the position of the latter, it corresponds closely to Targionia, but the structure of the thallus is extraordinarily simple, there being practically but two layers of cells with large irregular air-chambers between. While two sorts of rhizoids are present, those that represent the papillate type of the other Marchantiaceae, while thicker walled than the others, do not develop the projecting prominences. Indeed the whole structure of the plant is curiously reduced, and Leitgeb describes it as resembling the young plants of Marchantia or Preissia. The development of the sexual organs is but imperfectly known, and the suggestion of Leitgeb’s, that possibly the antheridium is reduced to a single cell, seems hardly probable in view of the structure of the rest of the plant. The sporogonium has the stalk and foot exceed¬ ingly rudimentary, but the upper part of the capsule shows a zone of cells whose walls are marked by peculiar ring-shaped thickenings, and opens regularly by a number of teeth, which on account of the thickened bars upon the cell wall offer a superficial resemblance to the peristome of the Bryineae. As in Targionia the archegonia arise near the apex of the ordinary shoots, and no proper receptacle is formed. 1 Leitgeb (7), vol. vi. p. 136. Ill MARC HA NT I EAR 69 All of the other forms have the archegonia borne upon a special receptacle, which, as the sporogonia develop, is raised upon a stalk. Here belong, according to Schiffner,1 sixteen genera with about 150 species. The receptacle may be, as we have seen, strictly dorsal in origin, or it may include the growing point of the archegonial branch, or finally it may be a branch system arising from the repeated dichotomy of the original growing point. Resume of the Marchantiacece Comparing the different members of this order, one is struck by the almost imperceptible gradations in structure between the different families, and this accounts for the difference of opinion as to where certain genera belong. That the Ricciacese cannot be looked upon as a distinct order is plain, and they may perhaps be bhst regarded as simply a family co-ordinate with the Corsiniese and Targioniese, and not a special group opposed to all the other Marchantiaceae. The gradual increase in complexity of structure is evident in all directions. First the thallus passes by all gradations from Riccia — with its poorly defined air- chambers with no true pores and single ventral lamellae, through Ricciocarpus and Tessalina , where definite air-chambers are present, opening by pores of the same form as those of the lower Marchantieae, and separate ventral scales occur — to forms like Marchantia, where the air-chambers are very definite and contain a special assimilating tissue, and the pores are of the cylindrical type. With this differentiation of the thallus is connected the segregation of the sexual organs and the development of special receptacles upon which they are borne. Finally, in the development of the sporogonium, while there is almost absolute uniformity in the earlier stages, we find a complete series of forms, beginning with Riccia , where no stalk is developed and all the cells of the archesporium develop spores, ascending through Tessalina , with a similar absence of a stalk, but the first indication of sterile cells, through the Corsiniece , to forms with a massive foot and elaters fully developed. It may be said, however, that there is no 1 Schiffner (1), p. 25. 7o MOSSES AND FERNS CHAP. Ill absolute parallelism between the development of the gameto- phyte and that of the sporophyte, for in Marchantia , the most specialised genus as to the gametophyte, the sporogonium is less developed than in the otherwise simpler Targionia and Fimbriaria. CHAPTER IV THE JUNGERMANNIACEHL A VERY large majority of the Hepaticas belong to the Jungermanniaceas, which show a greater range of external differentiation than is met with in the Marchantiacese, but less variety in their tissues, the whole plant usually consisting of almost uniform green parenchyma. In the lowest forms, eg. Amur a and Metzgeria , the gametophyte is an extremely simple thallus, in the former composed of almost perfectly similar cells, in the latter showing a definite midrib. Starting with these simplest types, there is a most interesting series of transitional forms to the more specialised leafy ones, where, however, the tissues retain their primitive simplicity. All of the Jungermanniaceae grow from a definite apical cell, which differs in form, however, in different genera, or even in different species of the same genus. Root-hairs are usually present, but always of the simple thin-walled type. The gametophyte, with the exception of the genera Haplo- mitrium , Calobryuvt, and Riella , is distinctly dorsiventral, and even when three rows of leaves are present, as in most of the foliose forms, two of these are dorsal and lie in the same plane, while the third is ventral. In the thallose forms, while the bilaterality is strongly marked, there is not the difference between the tissues of the dorsal and ventral parts which is so marked in the Marchantiacea;. In the lowest forms the gametophyte is a simple flat thallus fastened to the substratum by simple root-hairs, and develops no special organs except simple glandular hairs which arise on the ventral side near the apex, and whose mucilaginous secretion serves to protect the growing point. In Blasia and Fossonibronia we have genera 7 2 MOSSES AND FERNS CHAP. that, while still retaining the flattened thalloid character, yet show the first formation of lateral appendages which represent the leaves of the true foliose forms. In the latter the axis is slender, and the leaves usually in three rows and relatively large. The archegonia correspond closely in their development to those of the Marchantiacese, and in the lower (anacrogynous) forms arise in much the same way from surface cells of the dorsal part of the younger segments, and the apical cell is not directly concerned in their formation. The archegonia in these thus come to stand singly or in groups upon the dorsal surface of the thallus, whose growth is not interrupted by their development. In the higher leafy forms (Junger- manniaceae acrogynse) they occur in groups at the end of special branches, whose apical cell finally itself becomes the mother cell of an archegonium, and with this the growth in length of the branch ceases. The antheridia differ essentially in their first divisions from those of the Marchantiacese. After the first division in the mother cell, by which the stalk is cut off from the antheridium itself, the first wall in the latter, in all forms investigated except Sphcerocarpus and Riella , is vertical, instead of horizon¬ tal, and the next formed walls are also nearly vertical. The ripe antheridium is usually oval in outline and either nearly sessile or provided with a long pedicel. The spermatozoids are as a rule larger than in the Marchantiacese, and show more numerous coils, but like them are always biciliate. The embryo differs in its earliest divisions from that of the Marchantiacese. The first transverse wall divides the embryo into an upper and lower cell, but of these the lower one, except in Sphcerocarpus and Riella , takes no further part in the development of the sporogonium, but either remains undivided or divides once or twice to form a small appendage to the base of the sporogonium. In the upper cell the first wall may be either vertical (i.e. Pellia and most anacrogynous forms), or it may be transverse. From the upper of the two primary cells not only the capsule but the stalk and foot as well are formed. The development of these different parts varies in different forms, and will be taken up when considering these. All of the Jungermanniaceae, except the Rielleae, possess perfect elaters, but in the latter these are represented merely by sterile cells that probably serve simply for nourishing the IV THE J UN GERM A NNIA CE/E 73 growing spores. The sporogonium remains within the calyptra until the spores are ripe, when by a rapid elongation of the cells of the seta it breaks through the calyptra, which is left at its base, and the capsule then opens. The opening of the capsule is usually effected by its walls splitting into four valves along lines coincident with the first formed vertical cell walls in the young embryo. These valves, as well as the elaters, are strongly hygroscopic, and by their movements help to scatter the ripe spores. The latter show much the same differences observed in the Marchantiaceae. When the spores germinate at once they have abundant chlorophyll and a thin exospore, but where they are exposed to drying up, they have no chlorophyll and the exospore is thick and usually with characteristic thickenings upon it. From the . germinating spore the young gametophyte may develop directly, or there may be a well-marked protonemal stage. This latter is always found in the foliose forms, and is either a flat thallus, like the permanent condition of the lower thallose genera, or sometimes (. Protocephalozia ) it is a branched filamentous protonema, very much like that of the Mosses, and sometimes long-lived and producing numerous gametophores. Non-sexual reproductive bodies in the form of unicellular gemmae are found in many species, and in Blasia special receptacles with multicellular gemmae something like those of Marchantia occur. The Jungermanniaceae naturally fall into two well-marked series,1 J. anacrogynae and J. acrogynae, based upon the position of the archegonia. These in the former are never produced directly from the apical cell of a branch, in the latter group the apical cell of the archegonial branch always sooner or later becomes transformed into an archegonium. The Haplomitrieae show some interesting intermediate forms between the two groups, but all the other Jungermanniaceae examined belong decidedly to one or the other. As a rule the Anacrogynae are thallose (the “ frondose ” forms of the older botanists), but a few genera, especially Fossombronia, show a genuine formation of leaves. All the Acrogynae have a distinct slender stem with large and perfectly developed leaves. 1 Prof. L. M. Underwood proposes the name Metzgeriacese for the J. anacrogynae, reserving the name Jungermanniaceae for the J. acrogynae. These two groups he considers co-ordinate with the Marchantiaceae and Anthoceroteae. 74 MOSSES AND FERNS CHAP. J ungermanniacece A nacrogyncs The simplest form belonging here is Sphcerocarpus , a plant that shows certain affinities with the Ricciacese, but on the whole seems to be more properly placed at the bottom of the series of the Jungermanniacese. S. terrestris is a small plant growing upon the earth, usually in crowded patches, where, if abundant, Fig. 28 .-Stharocartus terrestris var. Cali/ornicus (Aust.). A, Male plant, X 40 ; 6, antheridia ; B, median section of a similar plant, X 80 ; C, the apex of the same section, X 240 ; A, ventral hair. it is conspicuous by the bright green colour of the female plants. The males are very much smaller, often less than a millimetre in diameter, and purplish in colour, so that they are easily ovci looked. 1 he thallus is broad and passes from an indefinite broad midrib into lateral wings but one cell in thickness (Fig. 28). The forward margin is occupied by a IV THE JUNGERMA NNIA CEsE 75 number of growing points formed by the rapid dichotomy of the original apex, and separated only by a few rows of cells. From the lower side of the thallus grow numerous root-hairs of the thin-walled form. The whole upper surface is covered with the sexual organs, each of which is surrounded by its own very completely developed envelope. A vertical section passing through one of the growing points (Fig. 2S, C) shows a structure closely like a similar section of Riccta. The apical cell (x) produces dorsal and ventral segments, and from the outer cells of the former the sexual organs arise exactly as in Riccia. On the ventral surface the characteristic scales of Riccia are absent, and are replaced by the glandular hairs found in most of the anacro- gynous Jungermanniaceae. The development of the archegonium shows one or two peculiarities in which it differs from other Hepaticae. The mother cell is much elongated, and the first division wall, by which the archegonium itself is separated from the stalk, is some distance above the level of the adjacent cells of the thallus, so that the upper cell is very much smaller than the lower one. The upper cell has much denser contents than the lower one, which instead of remaining undivided as in Riccia , divides into two nearly equal superimposed cells, this division taking place about the same time as the first division in the archegonial cell (Fig. 29, B). The divisions in the latter are the same as in Riccia, and the general structure of the arche¬ gonium offers no noteworthy peculiarities. The number of neck canal cells is small, probably never exceeding four, and in this respect recalls again Riccia. The central cell is relatively large, and the ventral canal cell often nearly as large as the egg. As the archegonium develops, its growth is stronger on the posterior side, and it thus curves forward. At first the young archegonium projects free above the surface, but presently an envelope is formed about it exactly as in Riccia, but arising at a later stage. After this has begun to form, its growth is very rapid, and it soon overtakes the archegonium and grows beyond it, and finally forms a vesicular body, plainly visible to the naked eye, at the bottom of which the archeg-onium lies. The formation of this involucre is quite o independent of the fertilisation of the archegonium, and as these peculiar vesicles cover completely the whole dorsal 76 MOSSES AND FERNS CHAP. surface of the plant, they give it a most characteristic appearance. Usually each archegonium has its own envelope, but Leitgeb 1 states that two or even more may be surrounded by a common envelope. When ripe, the venter of the arche¬ gonium is somewhat enlarged, but not so much as in Riccia. The egg-cell is very large, oval in form, and nearly fills the cavity of the single-layered venter. The first wall in the embryo is transverse, and divides the egg cell, which before division becomes decidedly elongated, into two nearly equal cells. Ordinarily in each of these cells A B. Fig. 29. Spharocarpus terrcstris var. Cali/omicus (Aust.). Development of the archegonium. A-C, Longitudinal sections, X 600 ; D, X 300. similai tiansverse walls are formed before any vertical walls appear, so that the embryo consists of a simple row of cells. As in the Marchantiacese the first wall separates the future capsule from the stalk, and in this respect Sphczrocarpus approaches the Marchantiacese rather than the Junger- manniaceae. Following the transverse walls there are formed in all the upper cells nearly median vertical ones, which are intersected by similar ones at right angles to them, so that in most cases (although this is not absolutely constant) the upper 1 Leitgeb (7), vol. iv. p. 6S. IV THE J UNGERM ANNIACEsE 77 half of the young sporogonium at this stage (Fig. 30, A) consists of two tiers, each consisting of four cells. The lower part of the embryo is pointed, and the basal cell either under- Fig. 30 .—SpJutrocarpus terrestris var. Cali/omictis. A, B, Median longitudinal sections of the archegonium venter, with enclosed embryos, X 260 ; C, an older sporogonium in median section, X 260 ; D, a still later stage, showing the large space between the archesporial cells and the wall, X 85. goes no further division or divides but once by a transverse wall, and remains perfectly recognisable in the later stages (Fig. 30, B, C). The other cells of the lower half divide much 78 MOSSES AND FERNS CHAP. like those of the upper half, but the divisions are somewhat less regular. There next arise in all the cells of the upper half periclinal walls, which at once separate the wall of the capsule from the archesporium. This wall in the later stages (Fig. 30, C, D) is very definite, and remains but one cell thick up to the time the sporogonium is mature. The further divisions in the capsule are without any apparent order, and result in a perfectly globular body composed of an outer layer of cells enclosing the archesporium, which consists of entirely similar cells with rather small nuclei and dense contents. While these changes are going on in the capsule, the lower part of the embryo loses its originally pointed form, and the bottom swells out into a bulb (the foot), which shows plainly at its base the original basal cell of the young embryo. This bulb is characterised by the size of the cells, which are also more transparent than those of the other parts of the embryo. Owing to the development of the stalk of the archegonium, after fertilisation the whole embryo remains raised above the level of the thallus, instead of penetrating into it, as is usually the case. The stalk or portion between the capsule and foot remains short, and in longitudinal section shows about four rows of cells. As the calyptra grows the upper part becomes divided into two layers, the part surrounding the foot into three. Instead of breaking through the calyptra at maturity, the capsule grows faster than the calyptra long before it is mature, and the upper part of the calyptra is first compressed very much and finally completely broken through by the enlarging capsule. Leitgeb 1 calls attention to the fact that soon after the cells of the archesporium begin to separate, the whole mass of cells becomes completely separated from the wall of the capsule, which grows rapidly until the cavity within is much larger than the group of archesporial cells, which thus float free in the large cavity. Fig. 30, D shows a section through a sporogonium at this stage. The cells making up the central mass are apparently alike, but Leitgeb 2 says that in the living sporogonium part of the cells have abundant starch and chlorophyll, while in the others these are wanting or present in much less quantity, while their place is taken by 1 Leitgeb (7), vol. iv. p. 70. 2 Leitgeb, l.c. IV THE JUNGERMA NNIA CEsE 79 oil, but that no rule could be made out as to the distribution of the two sorts of cells. The latter are the spore mother cells, while the others are gradually used up by the developing spoies. The latter remain united in tetrads, and escape from the capsule by the gradual decay of its wall and of the sur¬ rounding tissue of the gametophyte. The male plants are very much smaller than the females, with which they growr and under which they are at times almost completely hidden. The cell walls of the antheridial en\ elopes are often a dark purple-red colour, and this makes them much harder to see than the vivid green of the female plant. The apical growdh and origin of the antheridium is Fig. 31. — Sphcerocarpus terrestris var. Calif omicus. Development of the antheridium. A-D, Median longitudinal sections, X450; E, an older one, X225 ; F, a spermatozoid, killed with osmic acid, X 900. the same as in Riccia. The first division in the primary antheridial cell is the same as in that of the archegonium, but the basal cell is smaller, and does not divide again transversely, and takes but little part in the formation of the stalk. In the antheridium mother cell are next formed two transverse walls, dividing it into three superimposed cells. The twro uppermost divide, as in the Marchantiacese, by vertical median walls into regular octants, the lower by a series of transverse wralls into the stalk, which consists of a single row of cells sunk below the level of the thallus. After the division of the body of the antheridium into the octant cells, periclinal walls are formed in each of these, so that the body of the antheridium consists of eight central cells and eight peripheral ones, and the stalk 8o MOSSES ANE> FERNS CHAP. of two cells, of which the upper one forms the base of the antheridium body (Fig. 31, D). At this stage and the one preceding it Splicerocarpus recalls very forcibly the structure of the antheridium of the Characeae, although the succession of walls is not exactly the same. The divisions of the central cells are extremely regular, walls being formed at right angles, so that the sperm cells are almost perfectly cubical, and the limits of the primary central cells are recognisable for a long time. The development of the antheridial envelope begins much earlier than that about the archegonium, but in exactly the same way. By the time that the wall of the antheridium is formed the envelope has already grown up above its summit, and as the antheridium develops it extends far beyond it like a flask, at the bottom of which the antheridium is placed, and through whose neck the spermatozoids escape. These are very much like those of the other Hepaticse, and in size exceed those of most of the Marchantiaceae, but are smaller than is usual among the Jungermanniace^e. Leitgeb 1 studied the germination of the spores, which remain united in tetrads permanently. He found that all the spores of a tetrad were capable of normal development, which does not differ from that of Riccia or other thallose Liverworts. A more or less conspicuous germ tube is found at the end of which the young plant develops, one of the octants of the original terminal group of cells becoming, apparently, the apical cell for the young plant. The latter rapidly grows in breadth and soon assumes all the characters of the older plant. Leitgeb (Fig. 17, PL IX.) shows a condition that looks as if at an earlier stage a two-sided apical cell had been present, but he says nothing in regard to this. The sexual organs appear while the plant is extremely small. Leitgeb says he observed the first indications of them on individuals only one millimetre in diameter, and before the first papillate hair on the ventral surface had been formed. Corresponding closely in the origin and structure of the sexual organs to Splicer ocar pus, but differing much in habit, is the peculiar genus Riella, containing seven species, all sub¬ mersed aquatics, and, so far as is yet known, confined to Northern Africa and Southern Europe. The plant (Fig. 32, 1 Leitgeb (7), vol. iv. PI. IX. Fig. 17. IV 8i THE JUN GERM A NNIA CExE A) grows upright in the water, and consists of a central axis, about which a membranous expansion winds like the thread o a screw. Leitgeb 1 has carefully investigated the develop- Fig. 32 .—Riella helicofhylla (Mont.). A, A female plant enlarged; ?, sporogonia ; B, lateral, C, ventral view of the growing point, X 600 ; x, the apical cell ; L, leaves (after Leitgeb). ment of the thallus in R. helicophylla and R. Parisii, and found that the apical growth is like that of Sphcerocarpus , and that Leitgeb (7), vol. iv. p. 74. G 1 82 MOSSES AND FERNS CHAP. the peculiar wing is a dorsal growth (Fig. 32, B, C). Lateral leaf- like appendages are developed on either side of the growing point (Fig. 32, B, C). Both archegonia and antheridia resemble those of Sphcerocarpus very closely, and the structure of the capsule is also the same, no true elaters being developed, but instead these are simply sterile cells. Goebel 1 has recently made some further investigations upon the develop¬ ment of Riella , and believes that the origin of the growing point is secondary. His view is, however, based upon a study of secondary growths from the young thallus, as he was unable to procure very young germ plants.2 Aneura ( Riccardia ) and Metzgeria represent the simplest of the typical anacrogynous Jungermanniacese. In the former the thallus is composed of absolutely similar cells, all chloro¬ phyll-bearing, and in each cell one or more oil bodies, like those of the Marchantiaceae. In Metzgeria (Fig. 33) the wings of the thallus are but one cell thick, and there is a very definite midrib, usually four cells thick. The apical growth in both genera is the same, and is effected by the growth of a “ two- sided ” apical cell.3 The segmentation is very regular, especially in Metzgeria (Fig. 33), where each of the segments divides first into an inner and an outer cell, the former by subsequent divisions parallel to the surface of the thallus producing the thickened midrib, the outer cells dividing only by perpendic¬ ular walls, forming the wings. From the ventral surface of the young midrib papillae project, which curve up over the grow¬ ing point, in the form of short two-celled hairs, whose end cells secrete mucilage for its protection. In Aneura the growth is very similar, but all of the cells divide by walls parallel to the surface of the thallus, and no midrib is formed, and the thallus is several cells thick in all parts. In both genera numerous delicate colourless root -hairs are developed from the ventral surface, especially of the midrib, when that is present. Aneura is of interest as showing the only case among the Bryophytes of structures that may be compared to the zoospores of the green Alga. In A. multifida Goebel 4 dis- 1 Goebel (14). 2 On the fertilisation of the archegonium of Riella , see Kruch (1). “Two-sided is hardly a strict equivalent for the German “ zweischneidig,” but will be used here in the same sense, i.e. an apical cell from which two sets of lateral segments are cut off. 4 Goebel (8), p. 337. JV THE J UNGERM A NNIA CEsE 83 covered that the two-celled gemmae which had been described as formed simply by a separation of the cells of the thallus, were really formed within the cells and expelled from them through an opening, after which they divided into two cells and ultimately developed a young plant, much as an ordinary spore would do. The absence of cilia from these cells, which probably are the last reminiscences of the ciliated gonidia of Fig. 33. — Metzgeria pubescens (Radd.). A, Surface view of the thallus in process of division, X80 ; B, growing point of a branch showing the two-sided apical cell (.r) and the ventral hairs (/z), X 240 ; C, the grow'ing point in process of division, jr, a/, the apical cells of the two branches, X480. the aquatic ancestral forms, is to be accounted for by the terrestrial habit of Aneura. The branching is dichotomous, and is brought about by the formation of a second apical cell in one of the youngest segments. This apical cell is formed by a curved wall, which strikes the outer wall of the segment (Fig. 33, C). Thus two apical cells arise close together, and as segments are cut off from each, they are forced farther and farther apart, and 84 MOSSES AND FERNS CHAP. serve as the growing point of two shoots, which may continue to grow equally, when the thallus shows a marked forking (M. fur cat a), or one of the branches grows more strongly than the other, which is thus forced to one side and appears like a lateral branch (A. pinnatifida, Fig. 38, B). The sexual organs in both Anezira and Metzgena are borne on short branches, which in the latter arise as ventral structures, Fig. 34. — Aneui'ct pinnatifidci (Nees). A, Part of a thallus with two antheridial branches, slightly magnified ; B, an archegonial branch, X 40 ; C, cells from the margin of the archegonial branch showing the oil bodies ( o ), X 300. but in Aneura are simply ordinary branches that are checked in their growth by the production of the sexual organs, and not infrequently may grow out into ordinary branches after the formation of the sexual organs has ceased. In A. pinnatifida (Fig 34, B) archegonia and antheridia are usually produced upon separate branches, but may occur together. The origin of the antheridia can be readily followed in sections IV THE JUNGERMA NNIA CEHZ 85 made parallel to the surface of a male branch. The apex is occupied by an apical cell of the usual form, and the cell divisions in the young segment are extremely regular. The segment first di\ ides into an inner and an outer cell, and the former probably next into a dorsal and a ventral one. The dorsal cell divides by a longitudinal wall into two nearly equal cells, of which the inner one, dividing by a wall perpendicular to the first, gives rise to the primary' cell of the antheridium (Fig. 35, Ac?). This cell now projects above the surface of the thallus, and Fig. 35. — Aniura pinnatifida( Nees). A, Horizontal section of the apex of a young antheridial branch, X565; .r, the apical cell; antheridia ; B, transverse section of a young archegonial branch, passing through the apical cell (.r) ; young archegonia, X525; C, longitudinal section of a nearly ripe archegonium, X262; D, E, spermatozoids of Fcllia calycina , X1225 (D, E, after Guignard). divides into a single stalk cell, which undergoes no further divisions, and the antheridium mother cell. The divisions in the latter correspond to those in the other Jungermanniacese. First a vertical wall is formed, dividing the young antheridium into two equal parts. Next, in each of these, two walls arise, inter¬ secting each other as well as the median wall, and dividing each half of the antheridium into three cells, two peripheral ones and a central one. (A somewhat later stage than this is shown in Fig. 35, A.) The peripheral cells do not reach to 86 MOSSES AND FERNS CHAP. the top of the antheridium, and next a periclinal wall is formed near the top of the central cells, by which a third peripheral cell is formed in each half of the antheridium, which now con¬ sists of two central cells and six peripheral ones. The further divisions were not followed in detail, but seem to correspond with those in the higher forms. Of the two first cells into which the dorsal cell divides, the one which does not produce the antheridium, together with the inner of the two into which that cell first divides, form a partition which rapidly increases in height with the growth of the antheridia, and separates each from its neighbour by a single layer of cells, so that the antheridia are sunk in chambers, arranged in two rows, corresponding to the two series of segments of the apical cell. The archegonia are borne upon similar but shorter branches, and here too the development is very regular. In Fig. 3 5, B, a vertical section through the end of a young female branch is shown with the apical cell (x). Segments are here, too, cut off alternately right and left, and from each segment an arche- gonium develops. The segment is first divided, probably, as in the male branch and the vegetative ones, into an inner and an outer cell, but I did not succeed in getting satisfactory longi¬ tudinal sections parallel to the surface, so cannot speak posi¬ tively on this point. The youngest segment, in which the archegonium mother cell is recognisable, shows in- vertical sec¬ tion three cells, a small ventral one, a middle larger one, and a dorsal one — the archegonium mother cell. The latter does not form any stalk, but divides at once by the three intersect¬ ing walls, as in other Hepaticae, and the further development corresponds with these, except that the base of the arche¬ gonium is not free, and the central cell is below the level of the superficial cells of the thallus. The archegonium neck is short, and. the basal part as well as that part of the venter which is free, two cells thick (Fig. 35, C). The number of neck cells is small (apparently about four), but whether the number is constant cannot be stated positively. The female branch remains very short, and the archegonia, which are only produced in small numbers (usually not more than six to eight), are close together and surrounded by an irregular sort of envelope formed by the more or less incurved and very much laciniated margins of the branch. Secondary hair-like growths are also IV THE JUN GERM A NNIA CEs£ 87 formed, so that to the naked eye the archegonial receptacles appear as densely fringed and flattened tufts upon the sides of the larger branches. The earliest stages in the embryo are not perfectly known. Kienitz-Gerloff 1 investigated Metzgeria furcata and Leitgeb2 species of Aneura. In both of these the first division in the embryo separates an upper cell, from which capsule and seta de\ elop, from a lower cell, which forms a more or less conspicu¬ ous appendage at the base of the foot. The earliest divisions in the upper part are not known, but it soon becomes a cylindri¬ cal body consisting of several tiers of cells, each composed of c A B Fig. 36. — A, Young embryo of Aneura multijicla (Dum.), optical section, X235 (after Leitgeb) ;\B, median longitudinal section of an older sporogonium of A. pinguis (Dum.), X35 ; C, upper part of B, X20C ; spy sporogenous cells ; ely young elaters ; apical group of sterile cells. four equal quadrant cells. According to Leitgeb,3 the upper tier, from which the capsule develops, is formed by the first transverse wall in the upper part of the embryo. This upper tier is next divided by nearly transverse walls into four terminal cover cells, and four larger ones below, and these latter are again divided each into three cells, an inner one and two outer ones, so that the capsule consists of four central cells, the arche- sporium, and twelve wall cells (Fig. 36, A). A similar division in the lower tiers results in the formation of four axial rows and a single outside layer of cells in the stalk. In the lowest tiers the divisions are much less regular, and the first, 1 Kienitz-Gerloff (1). 2 Leitgeb (7), vol. iii. p. 47. 3 Leitgeb, l.c. 88 MOSSES AND FERNS CHAP. which is not very largely developed, shows no definite arrange¬ ment of the cells. The part of the wall of the capsule formed from the four cover cells later become two-layered, but the rest remains but one cell thick. In Metzgeria 1 the wall becomes later two - layered. The Fig- 37 •—Fossombronia longiscta (Aust.). A, Section through a young tetrad of spores ; B, surface view of the wall of a young spore ; C, two young elaters, X 6oo ; D, two ripe spores ; E, elater, x 300. archesporium divides first into two layers. In the upper cells the divisions are more regular than in the lower one, and later the archesporium is made up of cells arranged in more or less regular lines, starting from just below the apex and radiating from this point, extending to the base of the capsule. These cells are at first of similar form, and with the growth of the capsule become elongated with pointed ends that fit to¬ gether without any spaces between. Some of these cells, however, divide rapidly by transverse walls and give rise to rows of isodiametric cells (Fig. 36, sp), wedged in between others that have remained undivided (el). The former are the young sporogenous cells, the latter the elaters. A mass of cells lying just below the apex, and be¬ longing to the archesporium, remains but little changed, and forms the point of attachment for the elaters after the capsule opens (Fig. 36, B, C, m). The further development of spores and elaters is similar to that in the higher Marchantiaceae, and when the capsule is 1 Leitgeb (7), vol. iii. PI. II. Fig. 9. IV THE JUNGERMANNIACEjE 89 mature it opens by four valves which extend its whole length. The germination of the spores of Aneura has been studied by Kny 1 in A. palviata , and by Leitgeb J in A. pinguis, which agrees in all respects with the former. The spores, as is usual in the Jungermanniacese, have a poorly -developed exospore, and contain chlorophyll when ripe. Before any divisions take place, the spore enlarges to two or three times its original volume, and then elongates and by repeated cross-walls forms a filament of varying length. In the end cell next an inclined wall arises, which is met by another nearly at right angles to it, and thus the two-sided apical cell is established, and the thallus gradually assumes its complete form (Fig. 40, A). In the other thallose anacrogynous forms, i.e. Pallavicinia (Fig. 38, A), the sexual organs are borne upon the dorsal surface of the ordinary shoots, usually surrounded by a sort of involucre. In most of these forms the apical cell is of a different type from that of Aneura, but is variable even in the same species. Thus in Pallavicinia cylindrica , while the commoner form is nearly wedge-shaped, appearing four-sided seen from the surface, and triangular in vertical section, it may approach very nearly the two-sided type (Fig. 39, C). In the ordinary form four sets of segments are cut off, — -dorsal and ventral, as in Riccia or Sphcerocarpus , and two sets of lateral ones. In Pellia calycina the apical cell shows a similar form, but in P. epiphylla (Fig. 39, D, E) another type is seen. Here, while the surface view is the same as in P. calycina , in vertical section the cell is nearly semicircular, i.e. here there are but three sets of segments, two lateral ones and a basal one extending the whole depth of the thallus, and only later showing a division into ventral and dorsal cells. Probably this type has been derived from the former by a gradual in¬ crease in the size of the angle formed by the dorsal and ventral walls of the apical cell, which finally became so great as to practically form one plane. Janczewski3 followed very carefully the development of the archegonium in Pellia epiphylla, which differs a good deal from that of Aneura. The archegonia are formed in groups just back of the apex, but he does not seem to have been able to detect any relation between them and the segments of the 1 Kny (1). 2 Leitgeb (7), vol. iii. p. 48. 3 Janczewski (1), p. 389. 9° MOSSES AND FERNS CHAP. IV apical cell such as obtains in Aneura, but it seems probable that such a relation does exist. After the archegonium mother cell is cut off, it does not at once divide by vertical walls, but there is first cut off a pedicel, after which the upper cell under- Fic. 38.-A , Pallavicinia cylindrica (Aust.), x4; per, the elongated perianth; 13, Aneura. pinnatifii rr(L.), x6, 9, aichegonial branches; C-E, Fossombronia longiseta (Aust.). Xi • F Blasia pusilla (L.), X 4. goes the usual divisions. Of the three peripheral cells one is much smaller and does not as a rule divide longitudinally, so that the neck has normally but five rows of cells instead of six, as in the Marchantiaceae. Owing to the formation of the pedicel, Fig. 39. — A, Vertical, B, C, horizontal sections through the apex of P allavicinia cylindrica (Aust.), a-, apical cell, A, X225; B, C, X450; D, E, Pellia epiphylla (Nees); D, vertical section ; E, horizontal (optical) section, X450. 92 MOSSES AND FERNS CHAP. the archegonium is quite free at the base, and like that of Aneura the wall of the venter is two- layered. The neck becomes very long, and, according to Janczewski, the number of neck canal cells may reach sixteen or even eighteen. The antheridia of Pellia are larger than in Aneura , but in their development are similar except that the stalk is multi¬ cellular. The spermatozoids are the largest known among the Hepaticm (Fig. 3 5, D, E). In some species of Palla- vicinia the very strongly de¬ veloped midrib is made up in part of thick-walled elon¬ gated cells, but usually such cells are absent. The develop¬ ment of the sporogonium is best known in Pellia epi- phylla} Here the first wall, as in Aneura, separates a lower cell, which simply forms an appendage, from the upper cell, from which the stalk and capsule develop. In the latter the first wall is vertical, and is followed in each of the resulting cells by hori¬ zontal walls, by which the separation of the capsule from the seta is effected. These four cells are now divided by vertical walls, so that two layers of four cells each are present. The first periclinal walls in the apical group of cells separate the archesporium from the wall of the capsule. The differentiation of the capsule and seta follows as in Aneura , and the arrangement of the cells of the archesporium is much the same except that the rows of cells radiate from the base of the capsule and not from the summit. The foot is very distinct and forms a pointed conical cap, whose edges 1 Kienitz-Gerloff (1) ; Hofmeister (1). Fig. 40. — A, Young plant of Aneura palmata (Nees), X 265 (after Leitgeb) ; B, three views of a young plant of Pellia calycina, X420 (Leitgeb). IV THE J UNGERM A NNIA CERE 93 overlap the base of the seta. As in Targionia , and this is true for the other Jungermanniacem, the spore mother cells become deeply four-lobed before the division of the nucleus takes place. Farmer1 has recently studied this carefully in Pallavicinia decipiens and also in species of Aneura. In the former, previous to the division of the nucleus, there is formed a “ quadri-polar nuclear spindle,” which extends into each of the four divisions or lobes of the cell. Then follows a division of the chromosomes into four groups, apparently without the daughter nuclei first assuming the resting stage, and these four groups of chromo¬ somes travel to the four poles of the spindle and gradually as¬ sume the form of resting nuclei, after which the division walls are formed, completely dividing the cavity of the cell. The division of the nucleus occurs very late here, sometimes the thickenings upon the outside of the spores being indicated before the primary nucleus divides. In Aneura multifida , the formation of the quadri-polar spindle occurs, but there is after¬ ward a formation of two distinct nuclear figures of the ordinary type. The growth of the seta after the spores are ripe is ex¬ tremely rapid, but consists entirely in a simple elongation of the cells. Askenasi 2 has investigated this in Pellia epiphylla , and states that in three to four days the seta increases in length from about i mm. to in some cases as much as 80 mm., and that this extraordinary extension is at the expense of the starch which the outer cells of the young seta contain in great abundance, but which disappears completely during the elongation of the seta. The growing sporogonium here as well as in other species is strongly heliotropic. The calyptra in the thallose Anacrogynae is usually massive, and in addition there is formed about the growing sporogonium a special envelope inside the involucre, which in Pallavicinia especially (Fig. 38, A) becomes prolonged into a tube which completely encloses the sporogonium until just before its dehiscence. The further development of the spores and elaters corre¬ sponds with that of the Marchantiaceae (Fig. 37), and here there is the same method of the development of the thickenings upon the walls of the elaters and the spores. In cases where the spores germinate immediately, chlorophyll is developed and 1 Farmer (4). 2 Askenasi (1). 94 MOSSES AND FERNS CHAP. no proper exospore is formed, although the outer layer of the cell wall is more or less cuticularised. In the germination of the spores Pellia offers an exception to the other Jungermanniaceae, in that the spores divide into a multicellular body before they are discharged from the capsule. The presence of centrospheres in the dividing nuclei has been recently demonstrated by Farmer.1 The ripe spore here is an oval body which consists of several tiers of cells, the end cells being usually undivided, and the middle ones each consisting of four equal quadrant cells. There is some disagreement as to the earliest stages in the germination and the establishment of the apical growth. Hofmeister2 states that in P. epiphylla one end cell of the spore grows out into the first rhizoid, while the other develops into the growing point of the young plant. Muller, 3 on the other hand, states that in P. calycina both ends of the spore develop root-hairs while the growing point, which at first has a two-sided apical cell, like that of Metzgeria, arises laterally. Connecting the strictly thallose anacrogynous Hepaticae with the foliose acrogynous ones, are a number of most in¬ structive intermediate forms. Of these Blasia (Fig. 38, F) is perhaps the simplest. Flere the margin of the thallus is lobed, and these lobes, according to Leitgeb’s 4 view, are very simple leaves. In Fossombronia (Fig. 38, C, D), while the general thallose form is more or less evident, the leaves are unmistak¬ able, and as their development shows, morphologically the same as the leaves of the acrogynous forms. The most remarkable form, however, is Treubia insignis, a very large foliose Liverwort discovered by Goebel in Java. This has all the appearance of a very large acrogynous form, and also the typical three- sided apical cell ; but in regard to the position of the sexual organs it is typically anacrogynous. These and the Haplo- mitrieae form a perfect transition from the Anacrogynae to the Acrogynae. The multicellular gemmae of Blasia 5 have been alluded to. These are produced in long flask-shaped receptacles, and when mature form nearly globular brownish bodies whose cells contain much oil, and whose stalk consists of a simple row of cells. Among these are glandular hairs, which secrete mucilage, by the 1 Farmer (5). 2 Hofmeister (1), p. 21. 3 Muller, N. T. C. (1), p. 257. 4 Leitgeb (7), vol. i. p. 5. 3 Leitgeb, i.c. p. 5S. IV THE JUNGERMANNIACEM 95 swelling of which the gemmae are loosened from their pedicels, as in Marchantia. Similar but simpler gemmae having usually three cells occur in Treubia } Blasia is also characterised by the presence of colonies of Nostoc within the thallus. These occupy cavities in the bases of the leaves and are normally always present. The Haplomitriece The two genera, Haplovntrium and Calobryum , which consti¬ tute this family, differ from all other Hepaticae in having the leaves radially arranged, and not showing the dorsiventral form that characterises all the others. The plants are completely destitute of rhizoids but possess a rhizome-like basal part, from which the leafy axes arise. The latter have well -developed leaves arranged more or less distinctly in three rows. The stem grows from a tetrahedral apical cell, as in the acrogynous forms, but in Haplomitrium at least the apical cell does not develop into an archegonium. The archegonia are in this genus borne at the end of ordinary shoots, but in Calobryum the end of the female branch becomes much broadened and the numerous archegonia stand crowded together. In this case it is possible that the apical cell of the stem may finally produce an archegonium. Much the same difference is observable in the arrangement of the antheridia. Classification Jungermanniacese Anacrogynse. Apical cell of female axis never becoming transformed into an archegonium. A. Anelatereae. No true elaters, but sterile cells repre¬ senting these. Capsule cleistocarpous. Here belong the three genera, Thallocarpus , Sphcerocarpus , Riella. B. Elaterese. Capsule opening either by four valves or irregularly. Elaters always developed. a. Gametophore always dorsiventral, either strictly thallose or with more or less developed leaves. Families, — Metzgeriese, Leptotheceae, Codonieae. b. Gametophore upright with three rows of radially arranged leaves. Fam. I., Haplomitriea;. 1 Goebel (13). 96 MOSSES AND FERNS CHAP. The Hepaticce Acrogynce Treubia and Haplomitrium , as we have seen, connect almost insensibly the anacrogynous with the acrogynous Hepaticae. The latter are much more numerous than the former, but much more constant in form, and are doubtless a later specialised group derived from the former. While differing in the form and arrangement of the leaves and other minor details, they are remarkably constant in their method of growth and in the position of the sexual organs, especially the archegonia. These are always formed upon special branches, where, after a varying number of segments are cut off, the apical cell becomes the mother cell of an archegonium. The study of any typical form will illustrate the prin¬ cipal characters of the group. The species selected, Porella ( Mado - theca ) Bolanderi , is very like the common and widely distributed P. platyphylla, which corre¬ sponds with it in all structural points. The plant grows A, Female plant, x4; upon rocks especially, + j archegonial branches ; R, an open sporogonium, ^ * * * * x4 1 C, a male plant, X4; the antheridial branches. but also Upon the trunks of trees, and forms dense mats closely covering the substratum. It branches extensively, but always monopodially, dichotomous branching never occurring in the acrogynous Jungermanniaceae. The slender stem is com¬ pletely hidden above by the two rows of closely-set, overlapping, scale-like leaves. Upon the ventral side, which is fastened by scattering rhizoids to the substratum, there is a row of much smaller leaves ( Amphigastria), more or less irregularly disposed. 1 he dorsal leaves are nearly oval in outline, but the two- lobed form, that is very conspicuous in many species, is not so noticeable here. 1 he amphigastria are much smaller, and more elongated than the dorsal leaves. The structure of the leaf is IV THE J UNGERM ANNIA CEAG 97 of the simplest character, consisting of a single layer of polygonal cells containing numerous chloroplasts. The plants grow where they are exposed to alternate wetting and drying up. They may at any stage become completely dried up, and on being moistened will resume at once their activity. In the dried condition, the species under consideiation often remains for several months without -I~h D. 9 Pig. 42. — Porella Bolanderi (Aust.). A, Median longitudinal section of a vegetative axis; B, a cross-section of the apex of a similar one, x 500 ; jt, the apical cell ; h , hair ; d, dorsal surface*; v , ventral surface. apparently being injured in the least, and this power is shared to a considerable degree by most of the acrogynous forms, whose favourite habitat is the trunks of trees. The apical growth of the stem is extremely regular, and as in all the other acrogynous Hepaticae, the apical cell is a three-sided pyramid (Fig. 42, A). In longitudinal section it is much deeper than broad, and its outer face is almost flat. In cross-sections (Fig. 42, B) it has the form of an isosceles triangle, the shorter H 98 MOSSES AND FERNS CHAP. side turned toward the ventral surface of the plant. From this cell three sets of lateral segments are cut off, two dorsal and one ventral, and each of these gives rise to a row of leaves, a leaf corresponding to each segment of the apical cell. The first division wall in each segment is at right angles to its broad faces and divides it into two cells of somewhat unequal size. The next wall formed divides the larger of the two primary cells into an inner and an outer cell (Fig. 42, A), so that the young segment now consists of three cells, an inner one and two outer ; the latter in the dorsal segments correspond to the two lobes usually found in the dorsal leaves. The two outer cells now divide by walls in two planes, and rapidly grow out above the level of the apical cell and form lamellse which re¬ main single-layered, and undergo but little further modification beyond an increase in size. From the base of the young leaves simple hairs develop, but remain small and inconspicuous. The inner of the three first formed cells of the segment, by further division and growth in all directions, produces the axis of the plant. This in cross or longitudinal section shows almost perfectly uniform tissue. No distinct epidermis, or central strand, like that found in most Mosses, can be seen. The branching is monopodial and the branch represents the ventral lobe of a leaf. After the first division by which the two lobes of the leaf are separated, only the dorsal one develops into the lamina of the leaf, which is thus in the segment from which a branch is to form, only one-lobed. In the ventral cell three walls arise (Fig. 43), intersecting so as to cut out a pyramidal cell of the same form as the apical cell of the main axis, and the cell so formed at once begins to divide in the same way, and forms a lateral axis of precisely the same structure as the main one. The plants are strictly dioecious and the two sexes are at once recognisable. The males are smaller, and bear special lateral branches which project nearly at right angles from the main axis, and whose closely imbricated light green leaves make them conspicuous. At the base of each of the leaves is a long-stalked antheridium, large enough to be readily seen with the naked eye. The development of the antheridium may be easily traced by means of sections made parallel to the surface of the branch. At the apex (Fig. 42, C) is an apical cell much IV THE JUNGE RMA NNIA CE.E 99 like that in the sterile branches, but with the outer face more convex. The divisions in the segments are the same as there, but the whole branch remains more slender, and the hairs at the base of the leaves are absent. The antheridia arise singly from the bases of the leaves, close to where they join the stem, and are recognisable in the fourth or fifth youngest leaf (Fig. 42, C, ), X 14 (after Goebel). B, Gemma of Culolejcunia Gocbelii. numerous multicellular gemmae. This thallose condition is, however, only maintained during its vegetative existence. Previous to the formation of the sexual organs, the two-sided apical cell of a branch becomes three-sided, as in the young plant of other species of Lejeunia , and from this three-sided IV THE J UNGERM AN NI A CEAE 1 1 1 apical cell a short leafy branch, bearing the sexual organs, is produced.1 Considerable variety is exhibited by the leaves of the Acrogy nde as to their form and position, but all agree in their essential structure and early growth. The two lobes may be either equal in size or unequal. In the latter case either the dorsal or ventral lobe may be the larger, when the leaves are overlapping, as occurs in most genera. Where the dorsal half is the larger it covers the ventral lobe of the leaf in front of it, and the lea\es are said to be 1 mcubous ’ j where the reverse is the case, the leaves are “ suc- cubous.” These differences are of some importance in classification. In many species, especi¬ ally the tropical epiphytic forms, one lobe of the leaf frequently forms a sac - like organ, which appears to serve as a reservoir for moisture. These tubular structures some¬ times have the opening pro¬ vided with valves, which open readily inward, but not from the inside, and thus securely entrap small insects and crus¬ taceans which find their w*ay into them. Schiffner 2 com¬ pares them to the pitchers of a Sarracenia or Darlingtonia , and suggests that they may serve the same purpose. The branching of the foliose Jungermanniacese has been carefully investigated by Leitgeb, and will briefly be stated here. Two distinct forms are present, terminal branching and inter¬ calary. The former has already been referred to, but it shows some variations that may be noted. In most cases the whole of the ventral part of a segment, which ordinarily would produce the ventral lobe of a leaf, forms the rudiment of the branch, so Fig. 53. — Mastigobryum trilobatum (Nees). Longitudinal section of the stem, showing the endogenous origin of the branches ; x, the apical cell of the branch, X 245 (after Leitgeb). 1 For a complete account of these forms as well as others, see Goebel’s papers in the Annals of the Buitenzorg Botanical Garden, vols. vii. and ix., and in Flora, 1889 and 1893. 2 Schiffner (1), p. 65. I 12 MOSSES AND FERNS CHAP. that the leaf, in whose axil the branch stands, has only the dorsal lobe developed. In the other case, only a part of the cell is devoted to forming the branch, and the rest forms a diminished but evident ventral leaf-lobe, in whose axil the young branch is situated. The formation of the intercalary branches, which are for the most part of endogenous origin, may be illustrated by Mastigobryum, where the characteristic flagellate branches arise in this manner. Here the apical cell of the future branch (the branches in this case arise in strictly acropetal order) springs from the ventral segment, and exactly in the middle. It is distinguished by its large size, and is covered by a single layer of cells (Fig. 53). In this cell the first divisions establish the apical cell, which then grows in the usual way. The young bud early separates at the apex from the overlying cells, which rapidly grow, and form a dome-shaped sheath, between which and the bud there is a space of some size. Later the branch grows young more rapidly than the sheath and breaks r through it. The non-sexual reproduction of the acrogynous Hepaticae may be brought about either by the separation of ordinary branches through the dying away of the older parts of the stem, or in a few cases observed 1 new plants may arise directly from almost any point of a leaf or stem. Gemma; are known in a large number of species. These in most of the better known cases are very simple unicellular or bicellular buds arising often in great numbers, especially from the margins and apices of leaves. Curious discoid multicellular gemma; have been discovered in a number of species, especially in several tiopical ones investigated by Goebel.^ The gemma; upon the thallus of Lejeunia metzgeriopsis are of this character, and similar ones are found in Cololejeunia Goebelii. In the 1 Schiffner (1), p. 67. 2 Goebel (is)> IV THE JUN GERM A NNIA CETE 1 13 latter (Fig. 52, B) the gemma is a nearly circular cell plate attached to the surface of the leaf by a stalk composed of a single cell. The first wall in the young gemma divides it into two nearly equal cells, in each of which a two-sided apical cell is formed, so that like the gemma of Marchantia there are two growing points. There are usually four cells that differ from the others in their thicker walls and projecting on either side of the gemma above the level of the other cells. These serve as organs of attachment, perhaps by the secretion of mucilage, and by them the young plant adheres to the surface of the fern leaf upon which it grows. The development of the gemmae, whether unicellular or multicellular, follows very closely that of the germinating spores. Classification of the Jungerinanniacece Acrogynce In attempting to classify this immense family, great difficulties are encountered. While they show a considerable amount of variation, the differences are not constant, and the forms merge so one into another that a satisfactory subdivision of the group seems almost hopeless. In regard to essential characters, such as the growth of the stem, origin and structure of the sexual organs and sporogonium, they show remarkable uniformity, and evidently constitute a most natural group, allied very closely to the anacrogynous forms, as we have already attempted to show. The latest attempt to classify them is that of Schiffner,1 who confesses how difficult, perhaps impossible, a satisfactory arrangement is. He proposes eight subdivisions, as follows: I. Epigoniantheae ; IT Trigonantheae ; III. Ptilidioideae ; IV. Scapanioideae ; V. Stephaninoideae ; VI. Pleurozioideae ; VII. Bellincinioideae ; VIII. Jubuloideae. 1 Schiffner (i), p. 22. I CHAPTER V THE ANTHOCEROTE^E This order contains but three genera, Anthoceros , Dendroceros , and Notothylas, and differs in so many essential particulars from the other Hepaticse that it may be questioned whether it should not be taken out of the Hepaticse entirely and given a place intermediate between them and the Pteridophytes. All the members of the order correspond closely in the structure of the gametophyte, and while showing a considerable variation in the complexity of the sporophyte, there is a perfect series from the lowest to the highest in regard to the degree of develop¬ ment of the latter, so that the limits of the genera, which depend almost entirely upon the sporophyte, are difficult to determine. The Anthoceroteae are of extraordinary interest morphologically, as they connect the lower Hepaticie on the one hand with the Mosses, and on the other with the vascular plants. Leitgeb 1 has endeavoured to show that they are sufficiently near to the Jungermanniaceae to warrant placing them in a series with that order opposed to the Marchantiaceee, but a careful study of both the gametophyte and the sporophyte has convinced me that this view cannot be maintained ; and that while probably the affinities of the Anthoceroteae are with the anacrogynous Jungermanniaceae rather than with the Marchantiaceae, nevertheless the two latter orders are much nearer each other than the former is to either of them. The gametophyte in all the forms is a very simple thallus, either with or without a definite midrib. Of the three eenera Dendroceros is confined to the tropical regions, while the other 1 Leitgeb (7), vol. v. p. 9. CHAP. V THE ANTHOCERO TEAL ii5 genera occur in the temperate zones, but are more abundant in the warmer regions, where they also reach a greater size. The species of AniJioceros and Notothylas grow principally upon the ground in shady and moist places, and are not well adapted to resist dryness. A marked peculiarity of their structure is the character of the chloroplasts. There is as a rule but a single large flattened chloroplast in each cell, such as occurs in a good many con- tervoid Algae, eg. Coleochcete , Stigeoclonium , and others, but, so far as I know, is found elsewhere among the Archegoniatae only in certain cells of Selaginella. Simple thin - walled rhizoids are formed abundantly upon the ventral surface, where there are in many species curious stoma-like clefts which open into cavities filled with a mucilaginous secretion, and in some of which, in all species yet examined, are found colonies of Nostoc which form dark blue - green roundish masses, often large enough to be readily detected with the naked eye, and which were formerly 1 supposed to be gemmae. The sexual organs are very different from those of the other Hepaticae, and are more or less completely sunk in the thallus from the first. While the first divisions in the archegonium are much like those in the other Hepaticae, the subsequent ones are much less regular except in the axial row of cells, and the limits of the outer neck-cells are in the subsequent stages difficult to determine, and the archegonium projects very little above the surface of the thallus, even when- full grown. The divisions in the axial row of cells correspond to those in the other Archegoniatae. The origin of the antheridium is entirely different from that of all other Bryophytes, but shows, as will be seen later, certain suggestive resemblances to that of the lower Pteri- dophytes. Instead of arising from a superficial cell, as in all of the former, the antheridium, or in most cases the group of antheridia, is formed from the inner of two cells arising by the division of a superficial one. The outer one takes no part in the formation of the antheridia, but simply constitutes part of the outer wall of the cavity in which they develop. While the gametophyte is extremely simple in structure, being no more complicated than that of Aneura or Metzgeria , the sporophyte reaches a degree of complexity not equalled by 1 Hofmeister (1), p. 18. MOSSES AND FERNS CHAP. I 16 any of the other Bryophytes. Here, instead of the greater part of the sporogonium being devoted to spore formation, and the sporogonium dying as soon as the spores are scattered, the archesporium, especially in the higher forms, constitutes but a small part of the sporogonium, which develops a highly differentiated system of assimilating tissue, with complete stomata of the same type as those found in vascular plants ; and in addition a central columella is present whose origin and structure point to it as possibly a rudimentary vascular bundle. In all of them this growth of the sporogonium is not concluded with the ripening of the first spores, but for a longer or shorter time it continues to grow and produce new spores. This reaches its maximum in some species of Anthoceros , where the sporogonium may reach a length of several centimetres, and continues to grow as long as the gametophyte remains alive. In these forms the foot is provided with root-like processes, which are closely connected with the cells of the gametophyte, from which nourishment is supplied to the growing sporophyte. The archesporium produces spores and elaters, but the latter are not so perfect as in most of the Hepaticae. They often show a definite position with regard to the spore mother cells ; this is especially marked in Notothylas. The archesporium in all forms that have been completely investigated arises secondarily from the outer cells of the capsule. Leitgeb’s 1 conjecture that in Notothylas the whole central part of the capsule is to be looked upon as the archesporium, is not confirmed by my observations on N. valvata ( orbicularis ), where the formation of a columella and the secondary development of the archesporium are exactly as in Anthoceros'} It is hardly likely that in the other species there should be so essential a difference as would be implied by such an assumption. The development of the spores and their germination show some peculiarities which will be con¬ sidered when treating of these specially. The sporogonium shows no clear separation into seta and capsule, all except the foot and a very narrow zone above it producing spores. At maturity it opens longitudinally by two equal valves, between which the columella persists. The splitting is gradual and progresses with the ripening of the spores. 1 Leitgeb (7), vol. v. p. 49. 2 See also Mottier (2). V THE ANTHOCEROTE.E n 7 The type of the order, Anthoceros , includes fifteen to twenty species distributed over the world, but especially luxuriant in the tropics. The species that has been most studied is the cosmopolitan A. Icevis, which has been the subject of repeated investigations by numerous botanists. This species was carefully examined by the writer, as well as the larger A. fusiformis , a common Californian species allied to A. punctatus. The gametophyte is a fleshy dark -green or sometimes yellowish green thallus, which branches dichotomously, so that it often forms orbicular discs like those of the Marchantiaceae, but owing to the very rapid division of the growing points, and the irregular form of the margin, the individual apices are not usually recognisable. The thallus is either smooth, as in A. Icevis , or it is very much crisped and roughened by ridges and spines upon the upper surface. On cutting into the plant great quantities of colourless mucilage escape. Here and there, scattered through it, are dark blue -green specks, the Nos toe colonies always found in the thallus. Colourless root-hairs fasten it to the ground. No indications of the sexual organs can be seen from the outside, and it is sometimes difficult to procure them for study, as in both species their formation ceases very soon after the sporogonia begin to develop, and when these are large enough to be seen with the naked eye it is too late to procure the young sexual organs. The sporogonia are produced in great numbers, especially in A. fusiformis (Fig. 55, A), where they reach a length of 5 to 6 centimetres, or even more, and stand so closely together that a patch of fruiting plants has the appearance of a tuft of fine grass. In California the plants are annual. The spores germinate in the autumn with the commence¬ ment of the winter rains, and the sexual organs are mature by about the middle of January. As soon as fertilisation is effected the development of sexual organs ceases, and the regular apical growth stops, the margin of the thallus growing out irregularly beyond the young sporogonia, which are thus left some distance from the margin. After they are once formed they grow as long as the thallus remains alive, and this, in California, usually continues until about the 1st of May, when with the cessation of rain the thallus gradually dries up. I saw no evidences of the thallus surviving the dry season, as is the case with Riccia and Targionia. CHAP. V THE A NT HO CERO TEH 119 In order to study the apical growth satisfactorily, young plants that show no signs of the sporogonia should be selected. In A. fusiformis such a plant will show the margin of the thallus occupied by numerous growing points separated by a greater or smaller number of intervening cells. It is somewhat difficult to determine positively whether one or more apical cells are present. In sections parallel to the surface the initial cells are seen to occupy the bottom of a shallow depression (Fig. 56, C). In the case figured, .r probably is the single apical cell, and it seems likely that this is usually the case, although Leitgeb 1 was inclined to think that there were several marginal cells of equal rank. The outer wall of the cells shows a very marked cuticle. A vertical section passing through one of the growing points (Fig. 57) shows that the apical cell is much larger than appears from the transverse section. On comparing the two sections it is evident that its form is the same as in the Marchantiaceae or Pallavicinia. Two sets of lateral segments, and two sets of inner ones, alternately ventral and dorsal, are cut off, and the further divisions of these show great regularity, this being especially the case in the dorsal and ventral segments. Each of these first divides into an inner and an outer cell. The former divides repeatedly and in both segments forms the central part of the thallus. It is these cells that, according to Leitgeb,2 later show thickenings upon their walls somewhat like those met with in many Marchantiaceae. From the outer cells are developed the special superficial organs both on the ventral and dorsal sides. From the former arise the colourless delicate root-hairs and peculiar stoma-like organs, the mucilage clefts, first described by Janczewski,3 who also pointed out the true nature of the Nostoc colonies found within the thallus. These mucilage clefts, especially in their earlier stages, resemble closely the stomata of the higher plants. They arise by the partial separation of two adjacent surface cells close to the growing point, and often at least the two cells bounding the cleft are sister cells. However, the same division of the neighbouring cells frequently occurs without the formation of a cleft, and there is nothing to distinguish the two cells bounding the cleft from the adjacent ones, and a homology with the real stomata on the sporogonia is not to be assumed. The mucilage slit becomes 1 Leitgeb (7), vol. v. p. 13. 2 Leitgeb, l.c. 8 Janczewski (1). 120 MOSSES AND FERNS CHAP. V wider, and beneath it an intercellular space is formed which widens into a cavity whose cells secrete the abundant mucilage filling it. This mucilage escapes through the clefts and covers Fig. 56. — Anthoccros fusiformis (Aust.). A, Young plant with single growing point (jr), X85; B, horizontal section of the growing point of a similar plant, X525 ; x> the single apical cell; C, similar section of a growing point from an older plant, with possibly more than one initial cell, X260 ; D, a mucilage slit from the ventral side of the thallus, X525. the growing point in the same way as that secreted by the glandular hairs in the Jungermanniaceae. Each cell of the thallus contains a single chloroplast which may be either globular or spindle-shaped, or more or less 122 MOSSES AND FERNS CHAP. flattened. The nucleus of the cell lies in close contact with the chloroplast, and usually partly or completely surrounded by it. There is no separation of the tissues into assimilative and chlorophylless, as in the Marchantiaceae, and in this respect Anthoceros approaches the simplest Jungermanniaceae, as it does in the complete absence of ventral scales or appendages of any kind, except the rhizoids. The infection of the plant with the Nostoc has been carefully studied by Janczewski 1 and Leitgeb.2 The infection takes place while the plant is young, and is usually brought about by a free active filament of Nostoc making its way into the intercellular space below the mucilage slit, through whose opening it creeps. Once established, the filament quickly multiplies until it forms a globular colony. The presence of the parasite causes an increased growth in the cells about the cavity in which it lies, and these cells grow out into tubular filaments which ramify through the mass of filaments, and be¬ come so interwoven and grown together that sections through the mass present the appearance of a loose parenchyma, with the Nostoc filaments occupying the interstices. Other organisms, especially diatoms and Oscillarece, often make their way into the slime cavities, but according to Leitgeb’s investi¬ gations their presence has no effect upon the growth of the thallus. The plants are monoecious in A. fusiformis, and this is true of other species observed. In the former, however, the antheridia appear a good deal earlier than the archegonia. I observed them first on young plants grown from the spores, that were not more than 3 mm. in length. The exact origin of the cell from which the antheridia develop could not be made out, as none of my sections showed the youngest stages. Waldner’s 3 observations upon A. Icevis , however, and my own on Notothylas valvata, as well as a study of the older stages in A. fusiformis, leave no doubt that in this species as in the others the antheridia are endogenous, and the whole group of them can be traced back to a single cell. They arise close to the growing point, and the cell from which they arise is the inner of two cells formed by a transverse wall in a surface cell. The outer cell (see figure of Notothylas ) divides 1 Janczewski (1). 2 Leitgeb (7), vol. v. p. 15. 3 Waldner (2) ; see also Leitgeb (7), vol. v. p. 15. THE ANTHOCERO TEAL 123 v almost immediately by another wall parallel with the first, so that the group of antheridia is separated by two layers of cells from the surface of the thallus. The inner cell does not at once develop into an antheridium, at least in most species, although in the case of a doubtful species, probably A. Vincen- tiattus from New Zealand, Leitgeb 1 found normally but one antheridium in each cavity. The cell divides first by a longi¬ tudinal wall into two, each of which generally divides again, so that there are four antheridium mother cells, all, however, unmis¬ takably the product of a single cell, and if a comparison is to be made with the antheridium of any other Liverwort, the antheridium in the latter is homologous, not with the single one of Anthoceros, but with the whole group, plus the two¬ layered upper wall of the cavity in which they lie. The first divisions in the antheridium are the same as those in the original cell, i.e. the young antheridium is divided longi¬ tudinally by two intersecting walls, and the separation of the stalk from the upper part is secondary ; indeed in the earliest stages it is difficult to tell whether these longitudinal divisions will result in four separate antheridia or are the first division walls in a single one. Secondary antheridia arise later by budding from the base of the older ones, so that in the more advanced con¬ ditions the antheridial group consists of a varying number, in very different stages of development (Fig. 58). After the first transverse walls by which the stalk is separated, the next division in each of the upper cells is parallel to it, so that the body of the antheridium is composed of nearly equal octant cells. Then by a periclinal wall each of these eight cells is divided into an inner and an outer cell, and the eight central ones then give rise to the sperm cells, and the outer ones to the wall. The four stalk cells by repeated transverse divisions form the four-rowed stalk found in the ripe antheridium. The uppermost tier of the stalk has its cells also divided by vertical walls and forms the basal part of the antheridium wall. The transverse and vertical division walls in the central cells alter¬ nate with great regularity, so that there is little displacement of the cells, and up to the time of the separation of the sperm cells the four primary divisions are still plainly discernible, and the individual sperm cells are cubical in form. In the peri¬ pheral cells hardly less regularity is observable. Except near 1 Leitgeb (7), vol. v. p. 17. 124 MOSSES AND FERNS CHAP. the apex none but radial walls are formed after the first trans¬ verse wall has divided the body of the antheridium into two tiers, and when complete the wall consists of three well-marked transverse rows of cells, the lower being derived from the upper¬ most tier of stalk cells. At the apex the cells are not quite so regular (Figs. D, E). In its younger stages the antheridium is very transparent and perfectly colourless. In each peripheral cell a chloroplast is evident, but at this stage it is quite colour¬ less and the nucleus is very easily seen in close contact with it. Fig. 58. — A nthoceros fusiformis (Aust.). Development of the antheridium; D, E, drawn from living specimens, the others microtome sections ; D, j, shows the single chloroplast in each of the wall cells, and the secondary antheridium (j) budding out from its base ; 2 is an optical section of the same ; E, surface view of full-grown antheridium ; F, cross-section of a younger one. Figs. A, E X225, the others X450. As the antheridium grows the chloroplasts develop with it, becoming much larger and elongated in shape, and at the same time develop chlorophyll. The mature chloroplast is a flattened plate that nearly covers one side of the cell, and its colour has changed from green to a bright orange as in the antheridium of many Mosses. 1 he sperm cells are discharged through an opening formed by the separation of the apical cells of the antheridium. These cells do not become detached, and return to their original position, so that the empty antheridium has its THE ANTHOCEROTEsE 125 v wall apparently intact. The spermatozoids are small and entirely like those of the other Hepatics. Leitgeb 1 found in abnormal cases that the antheridia might arise superficially, as in the other Hepaticm. Whether this is a reversion to the primitive condition would be hard to say, but it is at any rate possible. At first the cell from which the antheridial complex arises is not separated from its neighbours by any space. About the time that the first divisions in it are formed, the young antheridial cells b. cichoraceus ■), while in others these are very much developed and the thallus has a more or less spongy texture, he. D. Javanicus. This development of the thallus and sporogonium has been studied only by Leitgeb,1 and in the main seems to correspond very 3 Leitgeb (7), vol. v. p. 39. V THE A NTHOCERO TEAE 139 closely to Anthoceros. A difference may be noted, however, in some details. Thus the form of the apical cell is like that of Pellia epiphylla , where the inner segments extend the whole depth of the thallus, and the division into dorsal and ventral segments is secondary. The formation of the wings begins near the apex and is the result of the growth of the marginal cells, which project strongly and divide rapidly by vertical walls only. The walls of the cells are thickened at the angles, and the surface view is curiously like a cross-section of the collenchyma of many vascular plants. As in Anthoceros mucilage slits are formed, sometimes on both surfaces of the thallus, and through these the plant is infected with Nostoc, as in the other Anthocerotere. In Dendroceros the Nostoc colonies are very large and cause conspicuous swellings upon the thallus. All the species of Dendroceros , according to Leitgeb, are monoecious, and the development of the sexual organs appears to be the same as in Anthoceros. The antheridia are very large and borne singly in cavities whose upper wall projects above the surface of the midrib. So far as is known the origin and development correspond closely to those of Anthoceros , except that the stalk is much longer and has but two rows of cells, which probably indicates that but one longitudinal wall is formed in the antheridial cell before the transverse walls that separate stalk and capsule. Gemmae occur in some species {D. cichoraceus , D. J avanicus), and are roundish cell masses developed from single cells of the lamina. So far as could be determined from incomplete material, the conclusion was reached by Leitgeb that Dendroceros approaches Anthoceros very closely in the development of the sporogonium. The origin of the columella, which usually in the later stages is composed of more than sixteen rows of cells, and the differentiation of the archesporium, seem to be exactly the same, and the further development of the large bulb-like foot and the formation of the spores and elaters are the same. The spores are larger, and the elaters (Fig. 74, B) provided with distinct spiral bands. In none of the species examined by Leitgeb did he find any traces of stomata upon the capsule, and concludes that they are entirely wanting in this genus, which in this respect, as well as in the character of the elaters, approaches closely one section of the genus Anthoceros. The spores, as in Pellia and Conocephalus , germinate within the capsule, and at the time of 40 MOSSES AND FERNS CHAP. dispersal are already multicellular. Apparently no germ tube is formed, but the spores develop at once into a cell mass upon which, while still very young, the mucilage clefts are developed, and at an early stage the infection by the Nostoc cells is effected. The growth of the older capsule and gradual develop¬ ment of the spores are the same as in Anthoceros. The third genus, Notothylas , is of especial interest, because it was largely upon the results of his investigations upon this plant that Leitgeb 1 based his theory of the close relationship of the Anthoceroteae and Jungermanniaceae. All of Leitgeb’s observations on the young capsule were made from herbarium material, and, as he himself admits, were in all cases embryos that had not fully developed. The writer has made a very complete examination of the commonest American species, N. orbicularis ( valvata ), and the results of the study of the development of the sporogonium differ so much from those of Leitgeb that they will be given somewhat in detail. The thallus much resembles a small Anthoceros, and sections through it show that in its growth and the development and structure of the sexual organs there is close correspondence. The thallus contains very large lacunae, which are formed in pretty regular acropetal order, and vertical sections show these large cavities increasing regularly in size as they recede from the apex. Similar but less regular lacunae occur in A. fusiformis. The antheridia arise as in Anthoceros, endogenously. The youngest stage found is shown in Fig. 68, A. Here evidently the young antheridia ( 6 ) have been formed by the longitudinal division of a single hypodermal cell, whose sister epidermal cell has divided again by a transverse wall to form the outer wall of the antheridial cavity (Figs. A, B). The commonest number of antheridia formed is four. Less regularity is found in the next divisions than in Anthoceros , although in the main they are the same. This is observable both in longitudinal and cross-sections (see Fig. 68, D). Ihe full-grown antheridium is more flattened than in either species of Anthoceros examined by me, and the stalk shorter and thicker, but otherwise closely resembles it, although the extremely symmetrical arrangement of the cells, especially of the wall, is much less noticeable. The archegonia correspond very closely, both in position 1 Leitgeb (7), vol. v. p. 39. V THE ANTHOCEROTE.E 141 and structure, with those of the other genera, the most marked peculiarity being the more nearly equal diameter of the cover cell and central cell, and a corresponding increase in the breadth of the neck canal cell. Subsequently the central cell becomes much enlarged and the appearance of the fully-developed arche- gonium is very much like that of Anthoceros (Fig. 69, A). As in A. fusiformis, the usual number of neck canal cells seems to be four, and in no case did the number exceed five. The cover cells were four in number in all the archegonia studied, and are Fig. 68. — Notothylas orbicularis (Sull.). Development of the antheridium. D, cross-section, the others longitudinal sections; E, nearly ripe antheridium, X300, the other figures X600; <5, A, the primary antheridial cells. larger than in Anthoceros. As in that genus, they are thrown off when the archegonium opens. The youngest embryo found was composed of four cells, and presented quite a different appearance from the corre¬ sponding stage in Anthoceros. It is impossible from this stage to tell whether the first wall in the embryo is vertical or trans¬ verse. This embryo consisted of four nearly equal quadrants, instead of having the two upper cells larger than the lower ones. By comparison with the older stages there is little doubt that here the first transverse wall separates the foot from the capsule, as in Sphcerocarpus , and that the upper cell 142 MOSSES AND FERNS CHAP. develops directly into the capsule instead of the latter being determined by the second transverse walls. In the next youngest stages found (Fig. 71, B) the archesporium was already differentiated. A comparison of this with the corre¬ sponding stage of Anthoceros shows conclusively that the two are practically identical in structure. The columella, evidently formed as in Anthoceros , and as there made up of four rows of cells, is surrounded by the archesporium cut off from the peri- a. i Fig. 69. Notothylas orbicularis (Sull.). Development of the archegonium, x6oo ; x, the apical cell. pheial cells. Leitgebs surmise that the columella is a second¬ ary formation is, therefore, for N. orlncu/aris at least, entirely erroneous, and it is extremely likely that when normal speci¬ mens ol the other species are examined from microtome sections, in the young stages at least, a similar columella will be found. The single embryo that Leitgeb 1 figures of N. orbicularis ( valvata ) is at once seen to be abnormal, and as his conclusions were drawn from a study of similar dead embryos 1 Leitgeb (7), vol. v. PI. IV. Fig. 77. V THE ANTHOCEROTE.E H3 in the other species, they cannot be accepted without more satisfactory evidence. While in the main corresponding to the embryo of A nthoceros there are some interesting differences which are closely associated with the structure of the older sporogonium. The foot is smaller than in Anthoceros and derived only from the lowest tier of cells. The columella is decidedly smaller, and the archesporium, as well as the young sporogonium wall, relatively much thicker. As in Anthoceros , the archesporium does not extend to the foot, but is separated by the zone of cells which there give rise to the meristem at the Fig. 70. — Notothylas orbicularis (Sull.). A, B, Horizontal sections of the growing point with young archegonia ; C, cross-section of the apex of an archegonium, showing the arrangement of the cover cells ; D, longitudinal section of a nearly ripe archegonium, X 400. base of the capsule. The form of the embryo is different too. It is pear-shaped and more elongated than in Anthoceros. As the embryo develops these differences become more apparent and others arise. Fig. 71, C shows a stage where the division of the archesporial cells has begun, and it is at once apparent how much more conspicuous they are. It is seen too that the outer cells of the upper part of the capsule are also dividing actively, and that, compared with Anthoceros, the apical part of the capsule retains its meristematic character for a much longer period. Corresponding with this, the growth at the base of the capsule is much less marked. The divisions in the archesporium are much more active than in Anthoceros, and also less regular. At first divisions occur in the upper portion in all directions, so that above the columella there is 144 MOSSES AND FERNS CHAP. a mass of archesporial tissue much thicker than that below, and occupying very much more space than the corresponding tissue in Anthoceros. Longitudinal sections through the basal part of the older sporogonium show an arrangement of tissues similar to those in Anthoceros , but there are differences corre¬ sponding to those in the young stages. The foot (Fig. 72, A) is much smaller and flatter, and sometimes shows a very regular structure. The central part is composed of a compact mass of rather large cells, between which and the base of the capsule is a narrow zone of meristematic tissue. The superficial cells do not always grow out into the root-like processes found in Anthoceros Fig. 71. — Notothylas orbicttlaris (Sull.). A, Four-celled embryo ; B, C, older embryos, in longitudinal section. The archesporial cells are shaded. A, X450; B, C, X225. and Dendroceros, but may remain short and project but slightly. The cells are characterised by abundant granular cytoplasm and conspicuous nuclei, showing that they are probably not only absorbent cells, but also elaborate the food materials taken in from the gametophyte. The gradual transition of the differen¬ tiated tissues above into the meristem at the base, is precisely as in Anthoceros, and sections at that point in the two genera can scarcely be distinguished from one another. The columella (in longitudinal section) in both shows four parallel rows of cells, outside of which lies the single row of archesporial cells, and four rows of cells belonging to the wall of the capsule. As the section is examined higher up, however, there are V 145 THE ANTHOCERO TETE marked differences, especially in the divisions of the arche- sporium. The first divisions in the archesporium of Notothylas L 146 MOSSES AND FERNS CHAP. 7 ic are periclinal, and for a short distance it is two-layered, as it is permanently in Anthoceros ; but still further up it widens very rapidly by the formation of repeated periclinal walls, and soon comes to be much thicker than either the columella or the capsule wall. A further study of the developing archesporium shows that the divisions occur with a good deal of regularity. The archesporial cells are divided by alternating vertical and trans¬ verse walls into four layers of cells instead of two, as in Anthoceros , and these cells are arranged in regularly placed transverse rows. At first the cells appear alike, but later there is a separation into sporogenous and sterile cells as in Anthoceros. Each primary transverse row of cells becomes divided into two. The upper row grows much faster, and its cells become swollen and the cytoplasm more granular, while the lower row has its cells remaining flattened and more transparent, i.e. there is a separation of the archesporium into alternate layers of sporogenous and sterile cells as in Anthoceros , but here the number of cells is double that in the latter, and the longer axis of the cells is transverse instead of vertical. In the portion of the archesporium above the colu¬ mella these alternate layers of spore mother cells and sterile cells extend completely across the cavity, and Leitgeb 1 has correctly figured this, although he probably was mistaken in assuming that this arrangement extended to the base of the capsule. The further development of the capsule is much like that of Anthoceros, but the division of the chloroplast takes place before the spore mother cells are isolated, and the primary chloro¬ plast is evident almost as soon as the sporogen¬ ous cells are recognisable as such. The cells of the columella do not become as elongated as in Anthoceros , and develop thicken¬ ings much like those of the sterile cells of the archesporium, and it was this partly that led Leitgeb 2 to the conclusion that even where a definite columella was present it probably arose as a secondary formation in the archesporium, similar 1 Leitgeb (7), vol. v. Pi. IV. Fig. 3a. 2 Leitgeb (7), vol. v. p. 50. Fig. 73. — Longitudinal section of a nearly ripe sporogonium of N. orbicularis, X50. THE ANTHOCEROTEjE 147 to the formation of the axial bundle of elaters in Pellia, and that in Notothylas as in the Jungermanniaceae, the arche- sporium arose from the inner of the cells formed by the first periclinal walls, and not from the outer ones. That this is not true for N. orbicularis is shown beyond question from sections of both the older and younger sporogonium, and it would be extremely strange if the other species should differ so radically from this one as would be the case were Leitgeb’s surmise correct. The wall of the capsule does not develop the assimilative apparatus of the Anthoceros capsule, and stomata are completely absent from the epidermis. The inner layers of cells are more or less completely disorganised, and they probably serve to nourish the growing spores, which here, of course, are corre¬ spondingly more numerous than in Anthoceros. As there, the sterile cells form a series of irregular chambers in which the spores lie. At maturity these sterile cells separate into irregu¬ lar groups (Fig. 74, C). Their walls are marked with short curved thickened bands, yellowish in colour like the wall of the ripe spores. At maturity the capsule projects but little beyond its sheath, and opens by two valves. In some species, e.g. N. melanospora , the capsule often opens irregularly. The Anthoceroteae form a most interesting series of forms among themselves, but are also of the greatest importance in the study of the origin of the higher plants. Unquestionably Notothylas represents the form which comes nearest to the other Liverworts, but until the other species are investigated further we shall have to assume that the type of the sporo¬ gonium is essentially different from that of the lower Hepaticae, and corresponds to that of the other Anthoceroteae. The primary formation of the columella and the subsequent differ¬ entiation of the archesporium occur elsewhere only in the Sphagnaceae. From Notothylas , where the archesporium con¬ stitutes the greater part of the older sporogonium, and the columella and wall are relatively small, there is a transition through the forms with a relatively large columella to Dendro- ceros, where the spore formation is much more subordinated and a massive assimilative tissue developed. In Notothylas the secondary growth of the capsule at the base, while it continues for some time, is checked before the capsule projects much beyond its sheath. In Dendroceros the growth continues much 148 CHAP. MOSSES AND FERNS longer, although it does not continue so long as in Anthoceros. The assimilative system of tissue in the latter is finally com¬ pleted by the development of perfect stomata, and the growth V THE ANTHOCERO TE.-E 149 of the capsule is unlimited. All that is needed to make the sporophyte entirely independent is a root connecting it with the earth. The Inter-relationships of the Hepaticce From a review of the preceding account of the Liverworts, it will be apparent that these plants, especially the thallose forms, constitute a very ill-defined group of organisms, one set of forms merging into another by almost insensible gradations, and this is not only true among themselves, but applies also to some extent to their connection with the Mosses and Pteridophytes. The fact that the degree of development of gametophyte and sporophyte does not always correspond makes it very difficult to determine which forms are to be regarded as the most primitive. Thus while Riccia is unquestionably the simplest as regards the sporophyte, the gametophyte is very much more specialised than that of Aneura or Sphcerocarpus. The latter is, perhaps, on the whole the simplest form we know, and we can easily see how from similar forms all of the other groups may have developed. The frequent recurrence of the two-sided apical cell, either as a temporary or permanent con¬ dition in so many forms, makes it probable that the primitive form had this type of apical cell. From this hypothetical form, in which the thallus was either a single layer of cells or with an imperfect midrib like Sphcerocarpus , three lines of development may be assumed to have arisen. In one of these the differenti¬ ation was mainly in the tissues of the gametophyte, and the sporophyte remained comparatively simple, although showing an advance in the more specialised forms. The evolution of this type is illustrated in the germinating spores of the Marchantiaceae, where there is a transition from the simple thallus with its single apical cell and smooth rhizoids to the complex thallus of the mature gametophyte. In its earlier phases it resembles closely the condition which is permanent in the simpler anacrogynous Jungermanniaceae, and it seems more probable that forms like these are primitive than that they have been derived by a reduction of the tissues from the more specialised thallus of the Marchantiaceae. Sphoerocarpus, showing as it does points of affinity with both the lower Marchantiaceae and the anacrogynous Jungermanniaceae, probably represents more nearly than any other known form 150 MOSSES AND FERNS CHAP. this hypothetical type. Its sporogonium, however, simple as it is, is more perfect than that of Riccia, and if our hypothesis is correct, the Marchantiaceae must have been derived from Sphcerocarpus- like forms in which the sporophyte was still simpler than that of existing species. Assuming that this is correct, the further evolution of the Marchantiaceae is simple enough, and the series of forms from the lowest to the highest very complete. In the second series, the Jungermanniaceae, starting with Sphcerocarpus , the line leads through Aneura , Pellia , and similar simple thallose forms, to several types with more or less per¬ fect leaves — i.e. Blasia, Fossombronia , Treubia, Haploviitrium. These do not constitute a single series, but have evidently developed independently, and it is quite probable that the typical foliose Jungermanniaceas are not all to be traced back to common ancestors, but have originated at different points from several anacrogynous prototypes. The systematic position of the Anthoceroteae is more difficult to determine, and their connection with any other existing forms known must be remote. While the structure of the thallus and sporogonium in Notothylas shows a not very remote resemblance to the corresponding structures in Sphcero¬ carpus, it must be remembered that the peculiar chloroplasts of the Anthoceroteae, as well as the development of the sexual organs, are peculiar to the group, and quite different from other Liverworts. To find chloroplasts of similar character, one must go to the green Algae, where in many Confervaceae very similar ones occur. It is quite conceivable that the peculiarities of the sexual organs may be explained by supposing that those of such a form as Sphcerocarpus , for example, should become coherent with the surrounding envelope at a very early stage, and remain so until maturity. In Aneura we have seen that the base of the archegonium is confluent with the thallus, in which respect it offers an approach to the condition found in the Anthoceroteae ; but that this is anything more than an analogy is improbable. The origin of the endogenous anther- idium must at present remain conjectural, but that it is secondary rather than primary is extremely likely, as we know that occasionally the antheridium may originate superficially. In regard to the sporogonium, until further evidence is brought forward to show that Notothylas may have the columella absent THE A NT HO CERO TETE v 1 5 1 in the early stages, it must be assumed that its structure in the Anthocerotese is radically different from that of the other Liverworts. Of the lower Hepaticai Sphcerocarpus perhaps offers again the nearest analogy to No to thy las, but it would not be safe at present to assume any close connection between the two. Of course the very close relationships of the three genera of the Anthoceroteae among themselves are obvious. On the whole, then, the evidence before us seems to indicate that the simplest of the existing Hepaticse are the lower thallose Jungermanniaceae, and of these Sphcerocarpus is probably the most primitive. The two lines of the Marchantiaceae and Jungermanniaceae have diverged from this common ancestral form and developed along different lines. The Anthoceroteae cannot certainly be referred to this common stock, and differ much more radically from either of the other two lines than these do from each other, so that at present the group must be looked upon as at best but remotely connected with the other Hepaticae, and both in regard to the thallus and sporophyte has its nearest affinities among certain Pteridophytes. The possi¬ bility of a separate origin of the Anthoceroteae from Coleochcete- like ancestors is conceivable, but it seems more probable that they have a common origin, very remote, it is true, with the other Liverworts. CHAPTER VI THE MOSSES (MUSCl) : SPHAGNACE^E - ANDRE.EACEE: The Mosses offer a marked contrast to the Hepaticai, for while the latter are pre-eminently a generalised group, the Mosses with a very few exceptions are one of the most sharply-defined and specialised groups of plants known to us. Although much outnumbering the Liverworts in number of species, as well as individuals, the differences in structure between the most extreme forms are far less than obtain among the Liverworts. While the latter occur as a rule in limited numbers, and for the most part where there is abundant moisture, the Mosses often cover very large tracts almost to the exclusion of other vegetation, especially in northern countries. In more temperate regions, the familiar peat-bogs are the best known examples of this gregarious habit. Mosses are for the most part terrestrial, and are found in almost all localities. Some grow upon organic substrata, especially decaying wood, and are to a greater or less extent saprophytic. Haberlandt1 first called attention to this, and investigated a number of forms, among them Rhynchostegium murale, Eurynchium pralongum , Webera nutans , and others, and in these found that the rhizoids had the power of penetrating the tissue of the substratum, much as a fungus would do. The most remarkable case, however, is Buxbaumia , where the leaves are almost completely absent and the saprophytic habit very strongly pronounced. Most of the Mosses, however, are abundantly provided with assimilative tissue, and grow upon almost every substratum, although most of them are pretty constant in their habitat. A number of species are typically aquatic, i.e. Fontinalis and many species of Sphagnum and 1 Haberlandt (4). ch.vi MOSSES (MUSC1) : SPHA GNA CE.E~ANDRE.EA CEAS 153 Hypnum ; others grow regularly in very exposed situations on rocks, eg. Andrecea. Very many, like Funaria hygrornetrica and Atnchum undulatum, grow upon the earth ; and others again, like species of Mmum and Thuidimn , seem to grow exclusively upon the decaying trunks of trees. Indeed Mosses are hardly absent from any locality except salt water. With the exception of the Sphagnaceae and Andreaeaceae, and possibly Archidium, the type of structure found among the Mosses is extraordinarily constant, and they may all be unhesitatingly referred to a single order, the Bryaceae, which includes within it an overwhelming majority of the species. 1 he gametophyte of the Musci always shows a well-marked protonema, which in most cases has the form of an extensively branching alga-like filamentous structure, from which later a distinct leafy axis arises as a lateral bud. In Sphagnum this protonema is a flat thallus, and the same is true of Tetraphis ancTa few other forms, but the filamentous protonema is very much more common. The gametophore arises from this protonema as a lateral bud, which develops a pyramidal apical cellTTrom which three sets of segments are cut off, each segment developing a leaf. The only exception to this, so far as is known at present, is the genus Fissidens } where the apical cell is wedge-shaped, and only two sets of segments are formed. Upon these leafy branches the sexual organs are borne. The relative degree of development of the protonema and the game¬ tophore differ much in different forms. Thus in the Phascaceae the protonema is permanent, and the gametophore small and poorly developed. In the higher ones, the protonema dis¬ appears more or less completely, and the assimilative functions are entirely assumed by the large highly developed gametophore, which is capable of reproducing itself by direct branching without the intervention of the protonema. The commonest form of gametophore is the upright stem with the leaves arranged radially about it, but in many creeping forms, such as some species of Mnium , Hypnum , etc., the gametophore is more or less dorsiventral ; but in these the apical cell is pyramidal, and produces three rows of leaves. Growing out from the base of the stem in most Mosses, and fastening it to the substratum, are numerous brown rhizoids which are not, however, morpho¬ logically distinct from the protonema. Thus if a turf of growing 1 Leitgeb (2). 154 MOSSES AND FERNS CHAP. Moss is turned upside down, the rhizoids thus exposed to the light very soon develop chlorophyll, and grow out into normal protonemal filaments. In most of the Mosses the leaves show a one-layered lamina traversed by a midrib, which may be quite small or very massive. This midrib is made up in part of elongated thick- walled sclerenchyma, and is obviously a conducting tissue. The highest grade of development of the leaf is met with in Polytrichum , where the midrib is very massive and peculiar vertical laminae of chlorophyll-bearing cells grow out from the surface of the leaf. In Buxbaumia the leaves are almost entirely abortive. The peculiar leaves of Sphagnum will be referred to later, as well as the details of structure of the leaves of other forms. The stem, except in the lowest forms, is traversed by a well-defined central strand of conductive tissue, and in a few of the highest ones, e.g. Polytrichum , there are in addition smaller bundles, continuations of the midribs of the leaves, recalling the “ leaf-traces ” found in the stems of Spermaphytes. The forms of non-sexual reproduction among the Musci are extraordinarily various, and a careful study of them shows that the morphological connection between the protonema and gametophore is a very intimate one, as they may arise recip¬ rocally one from the other. With the exception of certain resting buds developed from the protonema it appears 1 that the formation of the leafy stem is always preceded by the pro¬ tonema. The latter arises primarily from the germinating spores, but may develop secondarily from almost any part of the gametophore or even in exceptional cases from the cells of the sporophyte.2 From these protonemal filaments new gametophores arise in the usual way. The gametophore itself, especially where it is large and long lived, by the separation of its branches rapidly increases the number of new individuals. This is especially marked in Sphagnum , where this is the principal method of propagating the plants. Special organs of propagation in the form of gemmae also occur, and these may develop from the protonema or from the gametophore. Tetraphis pellucida (Fig. 105) is a good example, showing these specialised gemmae which after a time germinate by giving rise to a protonema upon which, as usual, the gametophore arises 1 Goebel (10), p. 170. 2 Pringsheim (2); Stahl (1). VI MOSSES {MU SCI): SPHA GNA CEJS — A NDREEEA CEAS 155 as a bud. In size the gametophore of the Mosses ranges from a millimetre or less in height in Buxbauniia and Ephernerum to 30 to 50 cm. in the large Polytrichaceae and Fontinalis. The branching of the gametophore is never dichotomous, and so far as is known the lateral branches arise, not in the axils of the leaves, but below them. Underground stems or stolons, which afterwards develop into normal leafy axes, are common in many forms, e.g. Climacium (Fig. 75). The sexual organs are borne either separately or together at the summit of the gametophoric branches. Where the plants are dioecious, it sometimes happens that the two sexes do not grow near together, in which case, although archegonia may be plentiful, they fail to be fecundated and thus no cap- 156 MOSSES AND FERNS CHAP. sules are developed. This no doubt accounts for the extreme rarity of the sporogonium in many Mosses, although in other cases, eg. Sphagnum , it would appear that the formation of the sexual organs is a rare occurrence. These resemble in general those of the Hepaticae, but differ in some of their details. The leaves surrounding them are often somewhat modified, and in the case of the male plants (. Atrichuin , P olytrichuni) different in form and colour from the other leaves, so that the whole structure looks strikingly like a flower. As a rule, the archegonial receptacles are not so conspicuous. The early divisions of the archegonium correspond closely with those of the Liverworts, but after the “ cover cell ” is formed, instead of dividing by cross walls into four cells, it functions for some time as an apical cell, and to its activity is due the entire development of the neck. The venter is usually very much more massive than in the Hepaticae, and the egg small. The antheridia, except in Sphagnum , are borne also at the apex of the stem, whose apical cell does not always, at any rate, become transformed into an antheridium, as we sometimes find, especially in species of Atrichum and Poly trichum, that the axis grows through the antheridial group and develops a leafy axis, which later may form other antheridia at its apex. Where the plants are dioecious the males are usually noticeably smaller than the females. The antheridia, except in Sphagnum , are very uniform in structure, and like the archegonium exhibit a very definite apical growth (Fig. 90). The wall remains one¬ layered, as in the Liverworts, and often the chloroplasts in its cells become red at maturity, as in some Liverworts, eg. Anthoceros. The ripe antheridium is in most Mosses club- shaped, and the sperm cells are discharged while still in connec¬ tion, the complete isolation of the sperm cells only taking place some time after the mass has lain in water. In Sphagnum the antheridia are much like those of certain leafy Liverworts, and stand singly in the axils of the leaves of the male branches. I he sporogonium of the Mosses reaches a high degree of development in the typical forms, and shows great uniformity, both in its development and in the essential structure of the full-grown sporophyte. With the exception of Sphagnum , which will be referred to more specially later, the early growth of the sporogonium is due to the segmentation of a two-sided apical cell. 1 he separation of the archesporium takes place at a late VI MOSSES (AfUSCI): SPHA GNA CESE — A NDRE/EA CEAL 157 period, and like that of Anthoceros it occupies but a very small part of the sporogonium, which in all the higher forms attains a considerable size and complexity. All the archesporial cells form spores, and no trace of elaters can be found. In all but the lower forms, the sporogonium becomes differentiated into a stalk (seta) and a capsule. This differ¬ entiation is gradual, and the elongation of the seta is not a rapid process, due simply to an elongation of the cells, but is caused by actual growth and cell division. In Sphagnum and Andrecea, where no seta is present, the axis of the gametophore elongates and forms a sort of stalk (pseudopodium), which carries up the capsule above the leaves. The separation of the capsule and seta takes place by a rapid enlargement of the upper part of the very much elongated embryo about the same time that the archesporium becomes recognisable. This enlargement is accompanied by a separation of the cells of two layers of the wall, by which an intercellular space is formed which later may become very large (Figs. 97-100). A second similar space may be formed inside the archesporium, but this is found only in the Polytrichacese. In the Sphagnaceae and Andreaeaceae this space is not found. These spaces are traversed by protonema-like filaments of chlorophyll-bearing cells, and the cells of the massive wall of the capsule also contain much chlorophyll, so that there is no question that the sporogonium is capable of assimilation. Stomata, much like those of Anthoceros or the vascular plants, occur upon the basal part of the capsule in many species, but are not always present. In Sphagnum and all the higher Bryacere the capsule opens regularly by means of a circular lid or operculum. This in the latter group is a most characteristic structure, and with its accompanying structures, the “ annulus ” or ring of thickened cells surrounding the opening of the rim, and the “ peristome,” — the fringe of teeth inside the annulus, — form some of the most important distinguishing marks of different genera and species. When ripe, the operculum falls off and the ripe spores are set free. The teeth of the peristome, by their hygroscopic move¬ ments, play an important part in scattering the spores, and physiologically take the place of the elaters of the Hepaticae. Some Mosses live but a few months, and after ripening their spores, die. This is the case with Funaria hygrometrica , 1,8 MOSSES AND FERNS CHAP. at least in California. Other Mosses are perennial, and some species of peat or tufa-forming Mosses seem to have an unlimited growth, the lower portions dying and the apices growing on until layers of peat or tufa of great thickness result, covered over with the still living plants whose apices are the direct continuation of the stems which form the basis of the mass. With the exception of a very few forms all the Mosses are readily referable to three orders. The first two, the Sphagnacese and the Andreseaceae, are represented each by a single genus, and are in several respects the forms that come nearest the Liverworts. All the other Mosses, except perhaps Archidium and Buxbaumia , conform to a very well - marked type of development, and may be referred to a common order, the Bryineae. The Phascaceae or cleistocarpous forms are sometimes separated from the higher Bryineae as a distinct order, but a study of their development shows that they belong to the same series, and only differ in the degree of development from the more specialised stegocarpous forms. Order I. Sphagnaceae The Sphagnaceae, or Peat-Mosses, are represented by the single genus Sphagnum. They are Mosses of large size, which, as is well known, often cover large tracts of swampy land and about the borders of lakes, forming the familiar peat-bogs of northern countries. Owing to the empty cells in the leaves and outer layers of the stem, they suck up water like a sponge, and the plants when growing are completely saturated with water. The colour is usually pale green, but varies much in depth of colour, and in many species is red or yellow. When dry the colour is much duller, largely owing to the opacity of the dry, emptyicelb which conceal to a great extent the colour of the underlying tissues, They branch extensively, and, according to Schimper, a branch is always formed corresponding to every fourth leaf ; but Leitgeb has shown that although this is the rule numerous exceptions to it occur. In sterile plants the branches are of two^ kinds, long flagellate branches which hang down almost vertical lylmd arc applied' to the stem, and much shorter ones that are crowded together at the apex ahd~h5Ve only a limited^growtW— The leaves are inserted on the stem by a broad base, and taper to a more or less well-marked point. VI MOSSES (MUSCI): SPHA GNA OEMS — A ND REM A OEM 159 According to Schimper, the divergence of the leaves of the main axis is always two-fifths, but on the smaller branches variations from this sometimes occur. The leaves show no trace of a midrib. As the axis elongates the leaves become separated, as c. Fig. 76. — Sphagnum (sp); A, B, Young protonemata, X262; C, an older protonema with a leafy bud (h), X about 40 ; 7, marginal rhizoids. well as the lower branches, but upon the smaller branches they remain closely imbricated. Root-hairs are present only in the earlier stages of the plant’s growth, and are only occasionally found in a very rudimentary condition in the older ones. The spores of Sphagnum on germination form first a very i6o MOSSES AND FERNS CHAP. short filament, which soon, at least when grown upon a solid substratum, forms a flat thallus, which at first sometimes grows by a definite apical cell.1 It first has a spatulate form (Fig. 76, A, B), which later becomes broadly heart-shaped, and closely resembles in this condition a young Fern prothallium, for which it is readily mistaken. The older ones become more irregular and may attain a diameter of several millimetres. The thallus is but one cell thick throughout its whole extent, and is fastened to the earth by colourless rhizoids. Later similar filaments grow out from the marginal cells of the thallus, and a careful examination shows that they are septate, and closely resemble the protonemal filaments of other Mosses. Like those, the septa, especially in the colourless ones, are strongly oblique. These marginal protonemal threads may, according to Hof- meister 2 and Schimper,3 produce a flattened thallus at their extremity, and thus the number of flat thalli may be increased. Schimper states that if the germination takes place in water, the formation of a flat thallus is suppressed and the protonema remains filamentous, but Goebel disputes this. In the few cases observed by me, only one leafy axis arose from each thalloid protonema, and although this is not expressly stated by Hofmeister and Schimper, their figures would indicate it. At a point, usually near the base, a protuberance is formed by the active division of the cells, in a manner probably entirely similar to that in other Mosses, and this rapidly assumes the form of the young stem. The first leaves are very simple in structure, and are composed of perfectly uniform elongated quadrilateral cells, all of which contain more or less chlorophyll. Like the older ones, however, they show the characteristic two- fifth divergence. Schimper states that the fifth leaf, at the latest, shows the differentiation into chlorophyll-bearing and hyaline cells, found in the perfect leaves. The first leaves in which this appears only show it in the lower part, the cells of the apex remaining uniform. At the base of the young plant very delicate colourless rhizoids are developed, and these show the oblique septa so general in the rhizoids of other Mosses. As the plant grows older these almost completely disappear. The apex of the stem and branches is occupied by a pyramidal apical cell with a very strongly convex outer free 1 Goebel (12), p. II. 2 Hofmeister (1). 3 Schimper (1). VI MOSSES {Mi/S Cl) : SPHA GNA CEAL— AND RE AS A CEAL 161 base. From the lateral faces of the apical cell, as in the acrogynous Liverworts, three sets of segments are formed. The u hole vegetative cone is slender, especially in the smaller branches. The first division in the young segment is parallel to its outer face, and separates it into an inner cell, from which Fig. 77-— Sphagnum cymbifolium (Ehrh.). A, Median longitudinal section of a slender branch; a-, the apical cell ; B, part of a section of the same farther down, showing the enlarged cells at the bases of the leaves, and the double cortex (cor); C, cross-section near the apex of a slender branch ; D, glandular hair at the base of a young leaf— all X525. the central part of the axis is formed, and an outer cell which produces the leaves and cortex. The second wall, which is nearly horizontal, divides the outer cells of the segment into an upper and a lower cell, the former being much broader than the latter, which is mainly formed from the kathodic half of the segment, which is higher than the anodic half.1 The next wall divides the upper cell 1 Leitgeb (1). M MOSSES AND FERNS CHAP. 162 into an upper and a lower one, the former being the mother cell of the leaf, the lower, with the other basal cell, giving rise to the cortex. Growth proceeds actively in the young leaf, which soon projects beyond the surface of the stem, and by the formation of cell walls perpendicular to its surface forms a laminar projection. The position of the cell walls in the young leaf is such that at a very early period a two-sided apical cell is established, which continues to function for a long time, and to whose regular growth the symmetrical rhomboidal form of the cells of the young leaf is largely due (Fig. 78). The leaves do not retain their original three -ranked arrangement, but from the first extend more than one-third of the circumference of the stem, so that their bases overlap, and the leaves become very crowded, and the two-fifth arrangement is established. The degree to which the central tissue of the stem is developed varies with the thickness of the branch. In the main stem it is large, but in the small terminal branches it is much less developed, as well as the cortex, which in these small branches is but one cell thick. Later the cortex of the large branches becomes two-layered (Fig. 77, B), and is clearly separated from the central tissue, whose cells in longitudinal section are very much larger. In such sections through the base of very young leaves characteristic glandular hairs are met with. They consist of a short basal cell and an enlarged terminal cell containing a densely granular matter, which from its behaviour with stains seems to be mucilaginous. The form of the secret¬ ing cell is elongated oval (Fig. 77, D), and the hair is inserted close to the base of the leaf, upon its inner surface. The young leaf consists of perfectly uniform cells of a nearly rhomboidal form (Fig. 78, A), and this continues until the apical growth ceases. 1 hen there begins to appear the separation into the chlorophyll-bearing and hyaline cells of the mature leaf. This can be easily followed in the young leaf, where its base is still composed of similar cells, but where toward the apex the two sorts of cells become gradually differentiated. The future hyaline cells grow almost equally in length and breadth, although the longitudinal growth somewhat exceeds the lateral. These alternate regularly with the green cells, which grow almost exclusively in length, and form a network with rhomboidal meshes, whose interstices are occupied by the hyaline cells. The latter at first contain chlorophyll, which VI MOSSES (. XIU SCI ): SPHA GNA CEJE—A NDREAEA CEAL 163 soon, however, disappears ; and finally, as is well known, they lose their contents completely, and in most cases round openings are formed in their walls. The protoplasm is mainly used up in the formation of the spiral and ring-shaped thickenings upon the inner surface of the wall, so characteristic of these cells Fig. 78. — Sphagnum cymbifolium (Ehrh.). A, B, C, Cells from the young leaf, X6oo; D, cells from a mature leaf; E, section of a similar leaf, X600; F, cross-section of an old stem, showing the thick, large-celled cortex, X about 50; G, sclerenchyma cells from the axial part of the stem, X600, MOSSES AND FERNS CHAP. 164 (Fig. 7 8, D). The chlorophyll cells are sometimes so crowded and overarched by the hyaline ones that they are scarcely perceptible, and of course in such leaves the green colour is very faint. Cross-sections of the leaves show a characteristic beaded appearance, the large swollen hyaline cells regularly alternating with the small wedge-shaped sections of the green cells (Fig. 78, E). Russow 1 has shown that the leaves of the sporogonial branch retain more or less their primitive character, and the division into the two sorts of cells of the normal leaves is much less marked. He connects this with the necessity for greater assimilative activity in these leaves for the support of the growing sporogonium. From his account too it seems that the stem leaves lose their activity very early. The degree of development of the thickenings upon the walls of the hyaline cells varies in different species, and in different parts of the leaf. It is, according to Russow,' best developed in the upper half of the leaf, where these thickenings have the form of thin ridges projecting far into the cell cavity. The development of the central tissue of the stem varies. The central portion usually remains but little altered and constitutes a sort of pith composed of thin-walled colourless parenchyma, which merges into the outer prosenchymatous tissue of the central region. The cells of the latter are very thick walled, and elongated, and their walls are usually deeply stained with a brown or reddish pigment. In their earlier stages, according to Schimper,3 the prosenchyma cells have regularly arranged and characteristic pitted markings on their walls, but as they grow older and the walls thicken, these become largely obliterated. Cross-sections of these prosen¬ chyma cells show very distinct striation of the wall (Fig. 78, G), which becomes less evident as they approach the thinner- walled parenchyma of the central part of the stem. No trace of a central cylinder of conducting tissue, such as is found in most of the Mosses, can be found in Sphagnum , and this is correlated with the absence of a midrib in the leaves. The cortex at first forms a layer but one cell thick, but is from the first clearly separated from the axial stem tissue. In the smallest branches it remains one-layered (Fig. 77, C), but in the larger ones it early divides by tangential walls into two layers, which at this stage are very conspicuous (Fig. 77, B). 1 Russow (4). " Russow, l.c. p. 8. 3 Schimper (1), p. 36. VI MOSSES (M USC I) : SPHA GNA CEAi — A NDREAEA CE/E 165 Later there may be a further division, so that the cortex of the main axes frequently is four-layered. W hile the cells of the young cortex are small, and the tissue compact, later there is an enormous increase in size of the cells, which finally lose their protoplasmic contents and resemble closely the hyaline cells of the leaves. Like the latter, the cortical cells are perfectly colourless, and usually have similar circular perfora¬ tions in their walls. T. he resemblance is still more marked in S. cymbifolium, where there are spiral thickened bands, quite like those of the hyaline leaf cells. On the smaller branches the cortical cells 1 have been found to be of two kinds the ordinary form and curious retort-shaped cells with smooth walls and a single terminal pore. The Branches Leitgeb2 has studied carefully the branching of Sphagnum , which corresponds closely to the other Mosses investigated. The branch arises from the lower of the two cells into \\ hich the outer of the two primary cells of the segment is divided. In this cell, which ordinarily constitutes part of the cortex, walls are formed in such a way that an apical cell of the ordinary form is produced. These lateral branches themselves branch at a very early period, and form tufts of secondaiy ones. Schimper was unable to make out clearly what the nature of this branching was, but suggested a possible dichotomy. Leitgeb, however, concludes that it is monopodial, and that each branch corresponds to a leaf, as do the primary branches. The growth of all the lateral branches, both the descending flagellate ones and the short upright ones at the top of the stem, is limited, and lasts through one vegetative period only. This, however, is not true of the branches that are destined to contain the axis. These are apparently morphologically the same as those whose growth is limited, but they continue to grow in the same manner as the main axis. fc> The Sexual Organs The sexual organs in Sphagnum are produced on branches that do not differ essentially from the sterile ones. The leaves of the antheridial branches are usually brightly coloured, red, 1 Schimper (1), p. 39- 2 LeitSeb (l)' MOSSES AND FERNS CHAP. 1 66 yellow, or dark green, and are closely and very regularly set, so that the branch has the form of a small catkin (Fig. 7 9, A). Pig. 79. A, Male catkin of Sphagnum cymlnfoliuiu, x 50 ; B, young antheridium of S', aeutifolium , x35°; C, opened antheridium of the same species; D, spermatozoid, X 1000 (about) ; E, female branch with sporogonium of V. aeutifolium , slightly magnified ; cal, calyptra. A, C, E, after Schimper ; B, after Leitgeb. The antheridia stand singly in the axils of the leaves, and Leitgeb 1 states that their position corresponds with that of 1 Leitgeb (4). VI MOSSES {M USC I) : SPHA GNA CEAE — ANDRE ALA CEsE 167 branches, with which he regards them as homologous, having observed in some cases a bud occupying the place of an antheridium. He studied in detail their development, which differs considerably from that of the other Mosses. The antheridium arises from a single cell whose position corresponds to that of a lateral bud on an ordinary branch. This cell grows out into a papilla and becomes cut off by a transverse wall. The outer cell continues to elongate without any noticeable increase in diameter, and a series of segments aie cut off from the terminal cell by walls parallel to its base, so that the young antheridium consists of simply a row of cells, comparable to the very young antheridium of the Marchanti- aceae. Intercalary transverse divisions may also arise, and later some or all of the cells, except the terminal one, divide by longitudinal walls, usually two intersecting ones in each cell, so that the antheridium rudiment at this stage is composed of a long stalk composed of several rows of cells, usually four, and a terminal cell which later gives rise to the body of the antheridium. The first divisions in the body of the antheridium only take place after the stalk has. become many times longer than the terminal cell, and is divided into many cells. The account of the development of the antheridium given by Hofmeister and Schimper is incomplete, and differs in some respects from that of Leitgeb. Neither of the former observers seems to have clearly recognised the presence of a definite apical cell from the first. Schimper1 states that after the stalk has been formed four rows of segments arise from the terminal cell ; to judge from the somewhat vague statements of Hofmeister'2 it appears that he regarded the terminal growth as taking place by the activity of a two-sided apical cell, as in other Mosses. Leitgeb states that, while this form of growth does frequently occur, usually the divergence of the seg¬ ments is not exactly half, and the segments do not stand in two straight rows, but some of them are intercalated be¬ tween these, forming an imperfect third row. Each segment is first divided by a radial wall into nearly equal parts, and these are then divided into an outer and an inner cell, and from the latter by repeated divisions the sperm cells are formed. The body of the full-grown antheridium is broadly oval, and 1 Schimper (1), p. 45- 2 Hofmeister (1), p. 154- MOSSES AND FERNS CHAP. 1 68 both in its position and shape recalls strongly that of such a foliose Liverwort as Porella. The development of the spermatozoids has been carefully followed by Guignard,1 and corresponds in the main with that of the Hepaticse. A peculiar feature is the presence of a pear- shaped amylaceous mass, firmly attached to the posterior coil. This becomes evident at a very early stage in the development and remains unchanged up to the time the spermatozoids are liberated (Fig. 79, D). The vesicle in which it is enclosed collapses, leaving only the large starch granule, which finally becomes detached. The free spermatozoid has about two com¬ plete coils, and in form recalls that of Chara. The cilia are two and somewhat exceed in length the body. The ripe antheridium is surrounded by a wreft of fine branching hairs, which Schimper suggests serve to supply it with moisture.2 It opens by a number of irregular lobes (Fig. 79, C), precisely as in Porella , and, like that, the swelling of the cells is often so great that some of them become entirely detached. Schimper states that antheridia may be formed at any time, but they are more abundant in the late autumn and winter. The archegonia are found at the apex of some of the short branches at the summit of the plant, and externally are indistinguishable from the sterile branches. The development of the archegonia has not been followed completely, but to judge from the stages that have been observed and the mature archegonium, its structure and development correspond closely to that of the other Mosses. As in these, and the acrogy- nous Hepaticae, the apical cell of the branch becomes an arche¬ gonium, and a varying number of secondary archegonia arise from its last - formed segments. The mature archegonium has a massive basal part and long somewhat twisted neck, consisting of six rows of cells. As in the other Mosses, the growth of the young archegonium is apical, and probably as there the neck canal cells are formed as basal segments of the apical cell, and the ventral canal cell is cut off from the central cell in the usual way. The venter merges gradually into the neck above and the pedicel below, and at maturity its wall is two or three cells thick. The egg 3 is ovoid, and 1 Guignard (i), p. 69. 2 These are probably the hyphse of a fungus. Wald ner (2). VI MOSSES {MU SC I) : SPHAGNA CEAL — ANDREASA CEAE 169 the nucleus shows a distinct nucleolus. Whether a recepthe spot is present is not stated. Mixed with the archegonia aie numerous fine hairs like those about the antheridium. The leaves immediately surrounding the group of archegonia latei Y Fig. 80 .—Sphagnum acutifolium (Ehrh.). Development of the embryo (after Waldner). A-D, Median optical section ; E, F, cross-sections. . A, D, E, -F, X360; C, X315; I>, X153. enlarge much and form a perichaetium. By the subsequent elongation of the main axis both archegonial and antheridial branches are often separated by the growth of the axis between them, although at first they are always crowded together at the top of the main stem. 170 MOSSES AND FERNS CHAP. The Sporogonium Waldner 1 has recently studied carefully the development of the embryo of Sphagnum , which differs essentially from all the other Mosses, and has its nearest affinity in the Antho- ceroteae. In the species A. acutifolium , mainly studied by Waldner, the sexual organs are usually mature in the late autumn and winter, and fertilisation occurs early in the spring. The ripe sexual organs are found in a perfectly normal condi¬ tion in mid-winter, under the snow, and apparently remain in this condition until the first warm days, when they open and fertilisation is effected. The first embryos were found late in February, and development proceeded from that time. The first division in the embryo is horizontal and divides it into two cells. In the lower of these the divisions are irregular, but in the upper one the cell walls are arranged with much regu¬ larity. The upper cell is the apical cell of the young embryo, and from it, by walls parallel to the base, a series of segments is formed (Fig. 80, A). These are usually about seven in number, and each of these segments undergoes regular divisions, these beginning in the lower ones and proceeding towards the apical cell, which finally ceases to form basal segments and itself divides in much the same way as the segments. The latter first divide by two vertical divisions into quadrants, and in each quadrant either directly by periclinal walls, or by an anticlinal wall followed by a periclinal wall in the inner of the two cells (Fig. 80, E), four central cells in each segment are separated from four or eight peripheral ones. The terms endothecium and arnphithecium have been given respectively to these two primary parts of the young Moss-sporogonium. By the time that the separation of endothecium and arnphithecium is com¬ pleted, a division of the embryo into two regions becomes manifest (Fig. 80, C). Only the three upper segments, in¬ cluding the apical one, give rise to spores ; the lower segments together with the original basal cell of the embryo form the foot, which in Sphagnum is very large. The cells of the foot enlarge rapidly and form a bulbous body very similar in appearance and function to that of Notothylas or Anthoceros. I he next divisions too in the upper part of the sporogonium 1 Waldner (2). VI MOSSES (MUSCI) : SPHA GNA CEAL — A NDREA2A CE/E 17 1 these forms. The central mass and origin, corresponds to the and the archesporium arises by the of the amphithecium into two layers by tangential the inner of these two layers, in contact with the becomes at once the archesporium. By rapid cell part of the sporogonium becomes globular, find their nearest analogies in of cells, both in position columella in these genera, division walls, and columella, division the upper and is joined to the foot by a narrow neck, much as in Notothylas (Fig. 81). The single - layered wall of the young sporogonium becomes six or seven cells thick, and the columella very massive. The one -layered archespor¬ ium also divides twice by tangential walls, and thus is four-layered at the time the spore mother cells separate. All the cells of the arche¬ sporium produce spores of the ordinary tetrahedral form. The so-called “ microspores ” have been shown conclu¬ sively to be the spores of a parasitic fungus.1 The layer of cells in immediate contact with the archesporium on both inner and outer sides has more chlorophyll than the neighbouring cells, and forms the “ spore-sac.” The ripe by a circular The epidermal actively than their which is the first indication the bottom other cells of the dry up and are very Fig. 81.— Median longitudinal section of a nearly ripe sporogonium of V. acutifolium , X24 ; ps, pseudopodium ; sp, spores ; col, columella (after Waldner). apsule opens d which is indicated long before it is mature, cells where the opening is to occui grow less neighbours, and thus a groove is formed of the operculum. The cells at ' the groove have thinner walls than the capsule wall, and when it ripens these readily broken, so that the operculum 1 "Mci wacrliin ( T 172 MOSSES AND FERNS CHAT1. is very easily separated from the dry capsule. Stomata, according to Schimper,1 always are present, sometimes in great numbers ; but Haberlandt 2 states that these are always rudimentary, and he regards them as reduced forms. No seta is formed, but its place is taken physiologically by the upper part of the axis of the archegonial branch, which grows up beyond the perichaetium, carrying the ripe sporogonium at its top (Fig. 79, E). The upper part of this “ pseudopodium ” is much enlarged, and a section through it shows the bulbous foot of the capsule occupying nearly the whole space inside it. The ripe capsule breaks through the overlying calyptra, the upper part of which is carried up somewhat as in the higher Mosses, while the basal part together with the upper part of the pseudo¬ podium forms the “ vaginula.” The disorganised contents of the canal cells, which are usually ejected from the archegonium, in Sphagnum remain in a large measure in the central cavity, and on removing the young embryo from the venter of the archegonium, this muci¬ laginous mass adheres to it and forms a more or less complete envelope about it, in which are often found the remains of spermatozoids. The species of Sphagnum are either monoecious or dioecious, but in no cases do archegonia and antheridia occur upon the same branch. The Andreceacece The second order of the Mosses includes only the small genus Andrecea, rock-inhabiting Mosses of small size and dark brown or blackish colour. In structure they are intermediate in several respects between the Sphagnaceae and the Bryineae, as has been shown by the researches of Kuhn 3 and Waldner,4 to whom wc owe our knowledge of the life-history of Andrecea. They all grow in dense tufts upon silicious rocks, and are at once distinguished from other Mosses by the dehiscence of their small capsules. These, like those of Sphagnum , are raised upon a pseudopodium, but are destitute of a true seta. The capsule opens by four vertical slits, which do not, however, extend entirely to the summit (Fig. 82). This peculiar form of dehiscence recalls the Jungermanniaceae, but is probably only 1 Schimper (1), p. 55. 2 Haberlandt (4), p. 475. 3 Kuhn (1). 4 Waldner (2). VI MOSSES {MU SCI): SPHA GNA CE/E — ANDRE.EA CEPE 173 an accidental resemblance. The closely-set stems branch freely ; the leaves, with three-eighth divergence, are either with a mid¬ rib (A. rupestris) or without one (A. petrophila). The growth of the stem is from a pyramidal apical cell, as in Sphagnum , and probably the origin of the branches is also the same as in that genus. The growth of the young leaves is usually from a two-sided apical cell, but another type of growth Fig. 82— Andrcaa petrophila (Ehrh.). A, Plant with ripe sporogonium, X to ; B, median section of nearly ripe capsule, X 80 ; ps, pseudopodium ; col , columella. is found where the apical cell is nearly semicircular in outline, and segments are cut off from the base only. These two forms of apical growth apparently alternate in some instances in the same leaf. The originally thin walls of the leaf cells later become thick and dark-coloured, whence the characteristic dark colour of the plant. The stem in cross-section shows an almost uniform struc¬ ture, and no trace of the central conducting tissue of the higher Mosses can be found. The outer cells are somewhat thicker- walled and darker-coloured, but otherwise not different from i7 4 MOSSES AND FERNS CHAl'. the central ones. Numerous rhizoids of a peculiar structure grow from the basal part of the stem, and from these, new branches arise which replace the older ones as they die away. These rhizoids are not simple rows of cells as in the Bryineae, but are either cylindrical masses of cells or flattened plates. These penetrate into the crevices of the rocks, or apply them¬ selves very closely to the surface, so that the plants adhere tenaciously to the substratum. Spores and Protonema The germination of the spores and the development of the protonema show numerous peculiarities. The spores may Fig. 83.— A, B, Germinating spores of A . petrophila, X200; C, protonema with bud (k) ; 1). joung archegonium in optical section ; E, 1, 2, two views of a very young embryo of A. crassinen’a, X 266 ; F, somewhat older embryo of A. petrophila ; G, older embryo showing the first archesporial cells ; H, I, cross-sections of young embryos, X200. A-D, after Kuhn ; E-I, after Waldner. germinate within a week, or sometimes remain unchanged for months, d hey have a thick dark-brown exospore and contain chlorophyll and oil. The first divisions take place before the exospore is ruptured, and may be in three planes, so that the young protonema then has the form of a globular cell mass ( Fig. 83, A). 1 his stage recalls the corresponding one in many of the thallose Hepaticm, e.g. Pellia , Radula, and is entirely different from the direct formation of the filamentous protonema of most Mosses. Some of the superficial cells of this primary tubercle grow out into slender filaments, either with straight or oblique septa, and these later ramify exten- VI MOSSES (MUSCI) : SPHA GNA CE.E ANDREW A CEAZ 175 sively. Where there are crevices in the rock, some of these branches grow into them as colourless rhizoids, but here, as in the Bryineae, there is no real morphological distinction between rhizoid and protonema. Most of the filamentous protonemal branches do not remain in this condition, but become trans¬ formed into cell plates or cylindrical cell masses, like the stem- rhizoids. The flat protonema recalls strongly that of Sphagnum , and is probably genetically connected with it. All of the different protonemal forms, except what Klihn calls the “ leaf¬ like structures,” vertical cell surfaces of definite form, can give rise to the leafy axes. The development of these seems to correspond exactly with that of the other Mosses, and will not be further considered here. The Sexual Organs The species of Andrecea may be either monoecious or dioecious. Archegonia and antheridia occur on separate branches, but their origin and arrangement are identical. The first-formed antheridium develops directly from the apical cell of the shoot, and the next older ones from its last-formed segments, but beyond this no regularity can be made out. In the first one the apical cell projects, and its outer part is separted from the pointed inner part by a transverse wall. This is followed by a second wall parallel to the first, so that the antheridium rudiment is composed of three cells. Of these the lower one takes little part in the future development. Of the two upper cells the terminal one becomes the body of the antheridium, the other the stalk. In the former, by two inclined walls, a two-sided apical cell is developed, and the subsequent growth is the same as in the Bryineae. The middle cell of the antheridium rudiment divides repeatedly by alternating trans¬ verse and longitudinal walls, and forms the long two-rowed stalk of the mature antheridium. On comparing the antheridium with that of the other Mosses, we find that it approaches Sphagnum in the long stalk, but in its origin and the growth of the antheridium itself, it resembles closely the higher Mosses. The first archegonium also is derived immediately from the apical cell of the female branch, and the first divisions are the same as in the first antheridium. Here, too, the subsequent development corresponds exactly with that of the highei 176 MOSSES AND FERNS CHAP. Mosses, and will be passed over for the present. The ripe archegonium shows no noteworthy peculiarities, and closely resembles in all respects that of the other Mosses. The Sporogoniuni The more recent researches of Waldner1 on the develop¬ ment of the sporogonium of Andrecea have shown clearly that here, too, the latter stands between the Sphagnaceae and the Bryineae. The first division in the fertilised ovum is transverse and divides it into two nearly equal parts. The lower of these divides irregularly and much more slowly than the upper one. In the latter (Fig. 83, E) the first division wall is inclined, and is followed by a second one which meets it nearly at right angles, and by walls inclined alternately right and left — in short, has the character of the familiar “ two-sided ” apical cell. The number of segments thus formed ranges from eleven to thirteen. Each segment is first divided by a vertical median wall into equal parts, so that a cross-section of the young embryo at this stage shows four equal quadrant cells. The next divisions correspond to those in Sphagnum, and result in the separation of the endothecium and amphithecium. The formation of the archesporium, however, differs from Sphagnum , and is entirely similar to that of the higher Mosses. Instead of arising from the amphithecium as in the former, the arche¬ sporium here is formed by the separation of a single layer of cells from the outside of the endothecium. All of the segments do not form spores, but only three or four, beginning with the third from the base. The two primary segments of the upper part of the embryo, like the corresponding ones in Sphagnum, go to form the foot, which is not so well developed, however, as in the latter. 1 he originally one-layered archesporium later becomes double, and as in Sphagnum extends completely over the columella, which is thus not continuous with the tissue of the upper part of the sporogonium. As in Sphagnum also, no trace of the intercellular space formed in the amphithecium of the Bryineae can be detected. A section of the nearly ripe capsule shows the club-shaped columella extending nearly to the top of the cavity. With the growth of the capsule the 1 Waldner (2). VI MOSSES (MUSCI): SP HA GNA CEAL—A NDREvEA CEPE 177 space between the inner and outer spore-sacs becomes very- large to accommodate the growth of the numerous spores. The pseudopodium is exactly the same as in Sphagnum , and the vaginula and calyptra are present. The latter is much firmer than in Sphagnum, and like that of the Bryineae. Archidium The genus Archidium is one whose systematic position has been long a subject of controversy. It has usually been associated Fig. 84. — Archidium Ravenelii (Aust.). A, Median section through a nearly ripe sporogonium, X90 ; B, base of the sporogonium, X270. with the so-called cleistocarpous Bryineae, but the researches of Leitgeb seem to point to a nearer affinity with Andrecea. The species of Archidium are small Mosses growing on the earth, and especially characterised by the small number, but very large size, of the spores contained in the sessile globular sporogonium. Hofmeister1 was the first to study the develop- 1 Hofmeister (i), p. 160. 178 MOSSES AND FERNS CHAP. ment, and his account agrees in the main with Leitgeb’s,1 except as to the relation of the columella and outer spore-sac. The first divisions in the embryo correspond exactly to those in Andrecea and the Bryineae, and for a time the young embryo grows from a two-sided apical cell. The secondary divisions in the segments, however, are quite different from that observed in any other Moss, and are like those in the antheridium. Instead of the first wall dividing the segment into equal parts, it divides very unequally. The second wall strikes this so as to enclose a central cell, triangular in cross-section, which with the corresponding cell of the adjacent segment forms a square. This square, the endothecium, does not therefore at first show the characteristic four-celled stage found in all other Mosses. The amphithecium becomes ultimately three-layered, and be¬ tween the second and third layers an intercellular space is formed, as in the Bryineae, but this extends completely over the top of the columella. The most remarkable feature, however, is that no archesporium is differentiated, but any cell of the endothecium may apparently become a spore mother cell. The number of the latter is very small, seldom exceeding five or six. They become rounded off, and gradually displace the other endothecial cells, which doubtless serve as a sort of tapetum for the nourishment of the growing spores. Each spore mother cell as usual gives rise to four spores, which are here very much larger than in any other Moss. A section of the ripe sporo- gonium (Fig. 81) shows that only one of the primary three layers of amphithecial cells can be recognised except at the extreme apex and base. The seta is present, and a foot, much like that of Andrecea , and penetrating into the tissue of the stem apex, is seen. Leitgeb is inclined to look upon Archidium as a primitive form allied on the one hand to Andrecea and on the other .to the Hepaticae, possibly Notothylas. However, as his assumption that the latter has no primary columella has been shown to be erroneous, his comparison of the whole endothecium of Archidium with that of Notothylas cannot be maintained, as we have shown that in the latter, as in Anthoceros, the archesporium arises from the amphithecium, and not from the endothecium, as is the case in Archidium. Inasmuch as the gametophyte and sexual organs of Archidium are those of the typical Mosses, it seems 1 Leitgeb (8). VI MOSSES (MU SCI) : SPHA GNA CE.E—A N I) REM A CEPE 179 quite as likely that the older view that Archidium is a degenerate form is correct. At any rate, until more convincing evidence can be brought forward in support of a direct connection between it and the Hepaticm than the formation of the spores directly from the central tissue of the sporogonium, it cannot be said that the question of its real affinities is settled. CHAPTER VII THE BRYINE/E Under the name Bryineae may be included all the other Mosses ; for although the so-called cleistocarpous forms are sometimes separated from the stegocarpous Mosses as a special order, the Phascaceae, the exact correspondence in the develop¬ ment of both the gametophyte and sporophyte shows that the two groups are most closely allied, the former being either rudimentary or degraded forms of the others. With few exceptions the protonema is filamentous and shows branches of two kinds, the ordinary green ones with straight transverse septa, and the brown-walled rhizoids with strongly oblique ones, but the two forms merge insensibly into one another, and are mutually convertible. In a few forms, notably the genus Tetraphis , the protonema is thalloid, and as in Sphagnum these flat thalli give rise to filamentous protonemal threads, which in turn may produce secondary thalloid proto- nemata. In some of the simpler forms, e.g. Ephemerum , the protonema is permanent, and the leafy buds appear as append¬ ages of it ; but in most of the larger Mosses the primary protonema only lives long enough to produce the first leafy axes, which later give rise to others by branching, or else by secondary protonemal filaments growing from the basal rhizoids. The early stages of development of the primary protonema are easily traced, as the spores of most Mosses germinate readily when placed upon a moist substratum. The ripe spores usually contain abundant chlorophyll and oil, and the thin exospore is brown in colour. The spore absorbs water and begins to enlarge until the exospore is burst, when the endospore pro¬ trudes as a papilla which grows out into a filament ; or the CHAP. VII THE bryineh: 181 endospore sometimes grows out in two directions, and one of the papillae remains nearly destitute of chlorophyll and forms the first rhizoid. The growth of the protonemal filaments is strictly apical, no intercalary divisions taking place except those by which lateral branches arise. If abundant moisture is present, the protonema grows with great rapidity and may form a dense branching alga -like growth of considerable extent. Sooner or later upon this arise the leafy gametophores. The development of the latter, as we have seen, also takes place Fig. 85. — Funaria hygroinctrica (Sibth.). A, Fragment of a protonemal branch with a young game- tophoric bud; r, rhizoid; B, median optical section of the bud ; C, older bud — 1, surface view ; 2, optical section ; x , apical cell ; D, protonema with a still older gametophore (gani) attached. A-C, X225; D, X36. abundantly from the secondary protonemal filaments which may be made to grow from almost any part of the gametophore. The development of the bud is as follows. From a cell of the protonema a protuberance grows out near the upper end. This is at first not distinguishable from a young protonemal branch, but it very soon becomes somewhat pear-shaped, and instead of elongating and dividing simply by transverse walls, the division walls intersect so as to transform it into a cell mass. After the cell is separated it is usually divided at once by a i82 MOSSES AND FERNS CHAP. strongly oblique wall, which is then intersected by two others successively formed and meeting each other and the first-formed one at nearly equal angles, so that the terminal cell of the young bud (Fig. 85, A) has the form of an inverted pyramid ; that is, by the first divisions in the bud the characteristic tetrahedral apical cell of the gametophore is established. From now on the apical cell divides with perfect regularity, cutting off three sets of lateral segments. From the base of the young gametophore the first rhizoid (Fig. 85, A, r) is formed at a very early period. The first two or three segments do not give rise to leaves, and the leaves formed from the next younger segments remain imperfect. Thus in Funaria hygrometrica these earliest formed leaves show no midrib. The young leaves rapidly elongate and completely cover up the growing point of the young bud, and are at first closely imbricated. Later, by the elongation of the axis, the leaves become more or less completely separated (Fig. 85, C, D). In Funaria , as well as in many other Mosses, buds are often met with that have become arrested in their development, lost their chlorophyll, and assumed a dark- brown colour. This arrest often seems to be the result of un¬ favourable conditions of growth, and under proper conditions these buds probably always will develop either directly or by the formation of a secondary protonema into perfect plants. Apical Growth of the Stem The growth of the stem of the fully-developed gametophore is better studied in one of the larger Mosses. The growth of the gametophore is so limited in length in Funaria that it is not so well adapted for this. Perhaps the best species for this purpose is the well-known Fontinalis antipyretica , which has already been carefully studied by Leitgeb.1 Amblystegium ripanum , var. fluitans , was examined by me and differed in some points from Leitgeb’s figures of Fontinalis. Fig. 86, A shows an exactly median longitudinal section through a strong growing point. Compared with Leitgeb’s figures the apical cell is much deeper than in Fontinalis , and in consequence the young segments more nearly vertical. Here, as in Sphagnum , the first wall in the young segment divides it into an inner and an outer 1 Leitgeb (1). VII THE HRYINE.E 18- cell, from the latter of which alone are formed the lateral appendages of the stem. The inner cells of the segments by repeated longitudinal and transverse divisions form all the tissues of the axis. The second division wall in the segment, like that in Sphagnum , is at right angles to the first, but in Amblystegium it extends the whole breadth of the segment. By this division the outer of the two primary cells of the segment is divided into an upper cell, from which the leaf develops, and a lower one, from which the outer part of the stem and the buds are Fig. 86. — A mblystegium riparium , var._fluita.us (Bruch and Schimp). A, Median longitudinal section of a strong shoot ; x, apical cell ; x' , initial of a lateral branch, X 250 ; B, transverse section through the apex, X250; C, similar section through a young branch, X500. formed. The leaves grow from a two-sided apical cell (Fig. 87), as indeed they seem to do in all Mosses, and the divisions pro¬ ceed with great rapidity and the young leaves quickly grow beyond and surround the growing point. In Amblystegium , as in all the typical Bryineae, the leaf has a well-developed midrib. The formation of this begins while the leaf is very young and proceeds from the base. In the middle row of cells (Fig. 87, C) a wall first arises parallel to the surface of the leaf, and this is followed by a wall in the cell on the lower side of the leaf MOSSES AND FERNS CHAP. 184 (Fig. 87, D). By further divisions in all the cells of this central strand the broad midrib found in the mature leaf is developed. In Amblystegium all the cells of the midrib are alike and have thickened walls. The midrib projects on both sides of the leaf, but rather more strongly upon the lower side. In Funana (Fig. 88) the structure of the midrib is more definite. Here two rows of cells take part in the formation of the midrib. Each of these first divides as in Amblystegium by a wall parallel to the surface of the leaf, so that in cross-section the central Fig. 87. — A mblystegium riparium , var. Jfuitans (Br. and Sch.). A, Longitudinal section of the stem passing through a young lateral branch (k) ; h , hair at the base of the subtruding leaf ; B, hori¬ zontal section of a very young leaf, showing the apical cell (.r) ; C, D, transverse sections of young leaves, showing the development of the midrib. All the figures X525. part of the leaf shows a group of four cells, those on the outer side being larger than the others. In the former the next wall is a periclinal one and divides the cell into an inner and an outer one. From the two inner cells by further division is formed the group of small conducting cells that traverse the centre of the midrib, while the outside cells together with those on the inner side of the midrib become much thickened and serve for strengthening the leaf. Here as in Amblystegium the lamina of the leaf remains single-layered, and its cells contain numerous large chloroplasts which, as is well known, continue VII THE HR YINEsE iS5 to multiply by division after the cells are fully grown. The marginal cells in the leaf of Funaria are much narrower than those between them and the midrib, and their forward ends Fig. 88. — Funaria hygromctrica (Sibth.). A, Transverse section of the apex of a young shoot, X515 ; B, C, cross-sections of young leaves, X515 ; D, cross-section of the stem, X25 7. often project somewhat, giving the margin of the leaf a serrate outline, which is also common in many other Mosses. The Branches For the study of the branching of the stem, Amblystegmm again is much better than Funaria , whose short stem and infrequent branching make it difficult to find the different stages. In Amblystegium , however, every median section will show some of the stages, and it is easy to follow out all the details, as has already been done in Fontinalis by Leitgeb.1 The lateral shoots originate from a basal cell of the segment below the middle of the leaf. It is very easily seen that it 1 Leitgeb (i). 1 86 MOSSES AND FERNS CHAP. belongs to the same segment as the leaf standing above it, and therefore is not axillary in its origin. The mother cell of the young branch projects above the surrounding cells, and in it are formed in succession three oblique intersecting walls which enclose the narrow pyramidal apical cell (Figs. 86, 87)- The secondary divisions in the first set of segments are not so regular as in the later ones, but the bud rapidly grows, and very soon the perfectly regular divisions of the young segments are established. So far as investigations have been made upon other genera, they follow the same line of development as Amblystegiuni , Fontinalis , and Sphagnum. Where the growth of the main axis is stopped by the formation of sexual organs, a lateral branch frequently grows out beyond the apex of the main axis, as in Sphagnum , and thus sympodia arise. In other cases, where the growth of the lateral branches is limited, characteristic branch systems arise, such as we find in Thuidium or Climacium (Fig. 75). Compared with Amblystegium , the growing point of Funaria and other Mosses of similar habit is much broader, and the apical cell not so deep. The arrangement of the segments is much the same, except that the original three-ranked arrange¬ ment of the segments which is retained in Fontinalis 1 is replaced in most Mosses by a larger divergence, owing to a displacement like that in Sphagnum. A cross-section of the older stem (Fig. 88, D) shows in most Bryineae a central cylinder of small thin - walled cells surrounded by a large-celled cortical tissue, which in the older parts of the stem often has its walls strongly thickened and reddish brown in colour. An epidermis, clearly recognisable as such, cannot usually be detected. The outer cells contain chlorophyll, which is wanting in the central cylinder. The rhizoids in Funaria grow mainly from the base of the stem, and the first ones arise very soon after the young bud is formed. Their growth, like that of the protonemal branches, is strictly apical, and they branch extensively. The young ends are colourless, but as they grow older the walls assume a deep brown colour. Usually the division walls in the rhizoids are strongly oblique. Their contents include more or less oil, and where they are exposed to the light, chlorophyll. 1 This is only strictly true in the smaller branches. VII THE BR YINEJE 187 The Sexual Organs Funaria is strictly dioecious. The male plants (Fig. 89, A) are easily distinguished by their form. They are about 1 cm. in height, with the lower leaves scattered, but the upper ones crowded so as to present much the appearance of a flower whose centre forms a small reddish disc. These male plants either grow separately or more or less mixed with the females. 1 88 MOSSES AND FERNS CHAP. Whether the first antheridium, as in Andreeva and Fontinalis , arises from the apical cell is doubtful, and it is impossible to trace any regularity in the order of formation of the very numerous antheridia. Except in very old plants, all stages of development are found together, and the history of the antheridium may be easily followed. A superficial cell projects above its neighbours, and this papilla is cut off by a transverse c D R Fig. 90 .—Funaria hygrometrica (Sibth.). Development of the antheridium. A-D, Longitudinal sections of young stages, x 600 ; D is cut in a plane at right angles to C ; E, optical section of an older stage, X 300 ; G, , cross-sections of young antheridia, X600 H, diagram showing the first divisions in the antheridium ; I, young spermatozoids, X1200. wall. I he outer cell either becomes at once the mother cell of the antheridium, or other transverse walls may occur, so that a short pedicel is first formed (Fig. 90, A). Finally in the terminal cell, as in Andreeva, two intersecting walls are formed enclosing a two-sided apical cell, from which two ranks of segments are cut off in regular succession (Figs. A, B, C). The number of these segments is limited, in Funaria not often exceeding seven, and after the full number has been formed, the VII THE BR YINE/E 189 apical cell is divided by a septum parallel with its outer face into an inner cell, which with the inner cells of the segments forms the mass of sperm cells, and an outer cell which produces the upper part of the wall. Before the full number is com¬ pleted, the secondary divisions begin, proceeding from the base upward. These are very regular, and correspond closely to those in the antheridium of the Jungermanniaceae, and can only be clearly made out by comparing transverse and verti¬ cal sections of the young antheridium. Fig. 90, H shows a diagram illustrating this : 1 is the wall separating two adja¬ cent segments, and 2 the first wall formed in the segment itself. The wall 2, it will be seen, starts near the middle of the periphery" of the segment and strikes the wall 1 far to one side of the centre, so that the segment is thus divided into two cells of very unequal size, although their peripheral extent is nearly equal. The next wall (3) strikes both the wall 1 and 2 at about equal distances from the periphery, and thus each segment is divided into an inner cell which in cross-section has the form of a triangle, and two peripheral cells. The latter divide only by radial walls, and give rise to the single-layered wall of the antheridium. The inner cells of the segments by further division in all directions form the mass of sperm cells. The first division wall in the central cell starts from near the middle of the segment wall and curves slightly, so that the two resulting cells are unequal in size. From this first division wall usually two others having a similar form extend to the peripheral cells, and these are next followed by others nearly at right angles to them. After this transverse and longitudinal walls succeed with such regularity that the limits of the primary segments remain perfectly evident until the antheridium is nearly full grown. The central cells in the fresh antheridium are strongly refringent, and in stained sections show a much more granular consistence than the outer ones. The nucleus, as in other cases studied, uses its nucleolus before the formation of the spermatozoids begins. The latter in their structure and development correspond with those of Sphagnum , but owing to their smaller size are not favourable for studying the minute details of development. In the peripheral cells are numerous chloroplasts which lie close to the inner wall of the cell in the ripe antheridium. A10SSES AND FERNS CHAP. 190 As the antheridium ripens, these gradually assume, a bright orange -red colour. The development of the stalk varies in different cases. Sometimes it consists of a row of several cells, sometimes the antheridium is almost sessile. The I' ic. 91. ]• unarm hygrometrica. (Sibth.). A, Antheridium that has just discharged the mass of sperm cells (B), X300; C, spermatozoids, X1300; D, paraphysis, X300; E, male “flower” of A trichum undu latum, x6 lowermost segments of the apical cell help to form the upper part of the stalk, and sometimes the two lowest seem to take no part in the formation of the sperm cells. There is no absolute uniformity in the cell divisions of the stalk, which VII THE HR VINE EE 191 varies in the arrangement of the cells in different individuals in the same inflorescence. If ripe antheridia are placed in water, they open within a few minutes. The peripheral cells become much distended, especially the terminal ones ; and the chromatophores being entirely confined to the inner part of the cells, the antheridium seems to be surrounded by a layer of perfectly hyaline cells. The dehiscence takes place at the summit between the terminal cells, which are simply separated without rupturing their walls. As soon as the mass of sperm cells is ejected, the opening closes completely and the empty antheridium looks very much as it did before, except that it is slightly contracted below. The whole mass of sperm cells is thrown out without separating the cells, and in this stage the walls of the sperm cells are still very evident. It sometimes happens that the mass is thrown out before the spermatozoids are complete, in which case they never escape. If, however, the spermatozoids are mature, they show active motion within the sperm cells while these are still in connection, and are set free by the gradual dissolution of the mucilaginous walls. The free spermatozoid is much like that of Sphagnum, but the body is somewhat shorter. The cilia are relatively very long and thick, and as in all Bryophytes but two in number. A small vesicle can usually be seen attached to the posterior end. Growing among the antheridia are found peculiar sterile hairs, or paraphyses. These in Funaria are very conspicuous, and consist of a row of cells tapering to the base, and very much larger at the apex. The terminal cell, or sometimes two or three of them, are almost globular in form and very much distended. All the cells of the paraphyses contain large chloroplasts which in the globular end cells are especially con¬ spicuous and often elongated with pointed ends. The archegonia are formed while the female plant is still very small, and it is much more difficult to recognise the female plants than the males. The archegonia are ripe at a time when the female plant is still but a few millimetres in height. In this case there is no doubt that the apical cell forms an archegonium directly, but not necessarily the first one, which arises usually from one of the last-formed segments. The elongation of the axis of the female branch is but slight, even in the later stages, and the plant remains bud-like even after the sporogonium is 192 CHAP. MOSSES AND FERNS developed. In regard to the development of the leafy axis, or gametophore, therefore, Funaria offers a very marked contrast to Fontinalis or Sphagnum , where the gametophore reaches such a large size and has practically unlimited growth. The young archegonia are quite colourless, and the details $ :P V ’ SBC Fig. 92.— Longitudinal section through the apex of a male plant of F. hygro/netrica, X300 ; L, leaf; S, antheridia ; /, paraphyses. of their structure may be made out without difficulty. The first division separates a basal cell from a terminal cell, which is the mother cell of the archegonium. In the latter three walls now arise, as in the Hepaticse and Andrecea , but in Funaria these do not all reach to the basal wall, but intersect at some distance above it, so that they enclose a tetrahedral cell, pointed below instead VII THE bryineh: 193 of truncate. This tetrahedral cell now divides by a transverse wall into an upper cell, corresponding to the “ cover cell ” of the Liverwort archegonium, and an inner one (Fig. 93, A), which gives rise, as in the Hepaticae, to the egg and ventral canal cell. From this point, however, the development proceeds in another way, and follows the method observed in Andrecea. o 194 MOSSES AND FERNS CHAP. The cover cell, instead of dividing by quadrant walls, has a regular series of segments cut off from it, and acts as an apical cell. These segments are cut off parallel both to its lateral faces and base, and thus form four rows of segments, the three derived from the lateral forces forming the outer neck cells, and the row of segments cut off from the base constituting the axial row of neck canal cells. Each row of lateral segments is divided by vertical walls, and forms six rows, which later divide by transverse walls as well, so that the number of cells in each row exceeds the original number of segments. This is not the case with the canal cells, which, so far as could be determined, do not divide after they are first formed. The wall of the venter owes its origin entirely to the three peripheral cells formed by the other primary walls in the archegonium mother cell. This becomes two-layered before the archegonium is mature, and is merged gradually into the massive pedicel, which in the Mosses generally is much more developed than in the Hepaticse, In the older archegonia the neck cells do not stand in vertical rows, but are somewhat obliquely placed, owing to a torsion of the neck during its elongation. From the central cell the ventral canal cell is cut off, as usual, but is relatively smaller than is usual among the Hepaticse. The egg shows a distinct receptive spot, which is not, however, very large. The rest of the egg shows a densely granular appear¬ ance, and the moderately large nucleus shows very little colour¬ able contents, beyond the large central nucleolus.1 The terminal cells of the open archegonium diverge widely, giving the neck of the archegonium a trumpet shape (Fig. 93, F). Usually some of the cells become detached and thrown off. The Embryo The first (basal) wall in the fertilised ovum divides it into an upper and lower cell, as in Sphagnum and Andrecea , and the next divisions correspond closely to those in the latter. In both cells a wall is formed intersecting the basal wall, but not at right angles. This is especially the case in the upper cell, where a second wall strikes the first one nearly at right angles, and establishes the two-sided apical cell by which the 1 It is perhaps questionable whether this mass is really the nucleolus. It may be composed in part of closely aggregated chromosomes. VII THE BRYINEsE !95 embryo grows for a long time. In the lower cell the divisions /. Fig. 94 —Funaria hygrometrica (Sibth.). Development of the embryo. A, Optical section of a very young embryo ; B, C, surface view and optical section of an older one, X 600 ; C, D, longitudinal sections of the apex of older embryos, X 600 ; cn, endothecium ; am, amphithecium. are somewhat less regular, but here also it is not uncommon 196 MOSSES AND FERNS CHAP. to find a somewhat similar state of affairs, so that the embryo may be said to have two growing points, although the lower end shows neither such regular nor so active growth as the upper one. In the latter the divisions follow each other with almost mathematical precision. There seems to be no rule as to how many segments are cut off from the apical cell before it ceases to function as such, but it is very much larger than in Andrecea, and the embryo soon becomes extremely elongated. A series of transverse sections of the young sporogonium shows very beautifully the succession of the first walls in the young segments. In a section just below the apex (Fig. 95, A), each Fig. 95.— Five transverse sections of a young embryo of F. hygromctrica. A, Just below the apex, the others successively lower down ; cn , endothecium, X 450. segment is seen to be first divided by a median wall into two equal cells. In Funaria usually the next division wall is periclinal, and at once separates endothecium and amphithecium. In most other Bryinese that have been examined, however, and this may also occur in Funaria (see Fig. 95, A), the second walls formed in the young segments are anticlinal, and it is not until the third set of walls is formed that the separation of endothecium and amphithecium is complete. The next divisions (Fig. 95, C) are in the amphithecium, and separate it into two layers. In the endothecium now a series of walls is formed, almost exactly repeating the first divisions in the original segment (Figs. D, E), and transforming it into a group VII THE BR YIN EH: 197 of four central cells and eight peripheral ones. Each of the latter divides twice by intersecting walls, so that a group of about sixteen cells (Fig. 96, A) occupies the middle of the endothecium. The eight peripheral cells divide by radial walls, after which each of these cells is divided by a periclinal wall into an outer and an inner cell (Fig. 96, B), and the outer cells divide rapidly by radial walls and form the archesporium. The single layer of cells immediately within, and therefore sister cells of the primary archesporial ones, is the inner spore-sac. The account of the development of the endothecium here Fig. 96.- -Three transverse sections of an older sporogonium of F. hygromctrica , X400 ; ar, archesporium; i, intercellular spaces. given differs slightly from the account of Kienitz-Gerloff. It was found first that there was not the absolute constancy in the number of cells given by him ; thus in Fig. 96, A there are only fourteen cells in the inner part of the endothecium, and although there are sixteen cells in the outer row their position is not perfectly symmetrical. Again the periclinal division of the cells of the inner spore -sac takes place later than he states is the case. In the eight primary cells of the amphithecium there first arise periclinal walls that divide each cell into an inner small 1 Kienitz-Gerloff (2). 198 MOSSES AND FERNS CHAP. VII cell in contact with the endothecium, and an outer larger one. This first division separates the wall of the capsule from the outer spore-sac. The latter next divides by radial and trans¬ verse walls, and later by periclinal walls into two layers (Fig. 96). Almost coincident with the latter, the rows of cells lying immediately outside it show a very characteristic appear¬ ance. They cease to divide, and with the rapid growth in diameter of the capsule become much extended both vertically and laterally, but are compressed radially. It is between these cells and the spore-sac that the characteristic air-space found in the capsule is formed. This is first evident shortly after the enlargement of the base of the capsule begins. The development can be very easily followed in longitudinal sections made at this stage. The formation of the space begins at the base of the capsule and proceeds toward the top. The line of cells bordering on the spore -sac is very easily followed, owing to their being so much larger than the neigh¬ bouring ones. As this is followed down, it is found that at the base of the capsule the cells are separated by large intercellular spaces, which become less marked toward the apex. With the rapid enlargement of the capsule these spaces become very large, and sections made a little later show that during this process the cells remain in contact at certain points, and form short filaments that extend across the space and unite the wall of the capsule with the outer spore-sac. At the base of the capsule the formation of intercellular spaces is not confined to the single layer of cells but involves the whole central mass of tissue, which becomes thus transformed into a bundle of filaments connecting the columella with the basal part (apophysis) of the capsule. The innermost of the two layers of cells between the archesporium and the air-space finally undergoes a second periclinal division, and in the full- grown sporogonium the archesporium is bounded on the outside by three layers of cells. The differentiation into seta and capsule takes place late in Funaria, and the first indication of this is the enlargement of a zone between the two, forming the apophysis, which at this stage (Fig. 97) is much greater in diameter than the upper part of the capsule. Sections through the apophysis and seta show a less regular arrangement of the cells than the sporiferous part of the capsule, but the general order of cell- Fig. 97 —Funaria. hygrometrica (Sibth.). A, Longitudinal section of a sporogonium showing the first differentiation of its parts, X about 96; B, the upper part of the same, X600 ; r marks the limits of the theca and operculum ; C, basal part of the capsule of the same, X600. The intercellular spaces are beginning to form ; ar, archesporium ; col, columella. 200 MOSSES AND FERNS CHAP. succession is the same, except for the formation of the arche- sporium. Almost as soon as the capsule is recognisable, the first indication of the operculum or lid becomes evident. About half-way between the extreme apex of the sporogonium and the top of the apophysis, a shallow depression is noticed extending completely round the capsule and separating the sharply conical apex from the part below. An examination of a longitudinal section at this point shows that at the point of separation the epidermal cells of the opercular portion are Fig. 98. Longitudinal section of an older capsule of F. hygrometrica ; i, intercellular spaces ; s/, archesporium ; r, cells between operculum and theca, X 523. much nai rower than those immediately below. Examining the tissues faither in, the archesporium is seen to extend only to a point opposite the base of the operculum, and the same is true of the row of large cells where the air-space is formed. If a similar section is made through an older capsule (Fig. 98) it is evident at once that the enlargement takes place mainly below the junction of the operculum, and there is also a similar but less pionounced increase in diameter in the operculum itself; but there is a narrow zone at the junction of the oper¬ culum and capsule, where the epidermal cells increase but VII THE BRYINEA ' 201 little in depth, while those above this point become very much larger and project beyond them. This narrow zone of cells marks the point where when ripe the operculum becomes detached. The latter, up to the time the sporogonium is ripe, is composed of a close tissue without any intercellular spaces. The epidermal cells, seen from the surface, are seen to be arranged in spiral rows running from the base to the apex. Its central part is made up of large thin-walled parenchyma, continuous with the tissue of the columella. The archesporium, therefore, is not continuous over the top of the columella, as in Sphagnum and Andrecea , but is cylindrical. The archesporium forms simply a single layer of small cells, and occupies a very small part of the sporogonium, much less, relatively, than in any of the forms hitherto described. Before the final division of the spores it divides more or less completely into two layers. The cells resulting from this last division are the spore mother cells, which separate soon after their formation and lie free in the space between the inner and outer spore-sacs, where each one divides into four tetrahedral spores. In the operculum, as the capsule approaches maturity, the differentiation of annulus and peristome takes place. The former consists of about four rows of cells (Fig. 98) that occupy the periphery of the broadest part of the operculum. These cells are very much compressed vertically, but are deep and have their walls thicker than their neighbours. Just below them are about two rows of similar cells, but somewhat less compressed and with very thin walls. These latter cells mark where the separation takes place, the annulus forming the rim of the loosened operculum. The peristome arises from the fifth layer of cells from the outside of the operculum. If a median longitudinal section of a nearly ripe capsule is examined, the row of cells belonging to this layer (Fig. 99, per) is at once seen to have the outer walls strongly thickened, and this thickening extends for a short distance along the transverse walls. The inner walls of the cells also show a slight increase in thickness, but much less marked than the outer ones. A similar thickening of the cell walls occurs also in about three rows of cells which run from the outside of the capsule to the base of the peristome, and form the rim of the “ theca ” or urn. The epidermis of the whole capsule has its outer walls 202 MOSSES AND FERNS CHAP. very much thickened, and upon the apophysis are found stomata quite similar to those found upon the sporogonium of Anthoceros or the leaves of vascular plants. Haberlandt 1 showed that while the form of the fully -developed stoma in Funaria differs from that of most vascular plants, this difference is secondary, and that in its earlier stages no difference exists. This can be easily verified, and with little difficulty all the different stages found. The young stoma B. Fig. gg. A, Longitudinal sections of a nearly ripe capsule of F. liygrometrica , X 260 ; per, peristome • r annulus ; t, thickened cells forming the margin of the theca ; B, the sporogenous cells shortly before the final divisions ; z, inner ; o, outer spore-sac, X 525. (Fig. 1 01) has the division wall extending its whole length, as is the case in stomata of the ordinary form. As the stoma grows larger, however, the median wall does not grow as fast as the lateral walls, and a space is left between its extremities, so that the. two guard cells have their cavities thrown into communication, and the division wall forms a cellulose plate extending, from the lower to the upper surface of the stoma, but with its ends quite free. The formation of the pore by the splitting of the middle lamella of the division wall takes 1 Haberlandt (4), p. 464. VII THE BRYINEAi 203 place in the ordinary way. Later the walls of the epidermal cells become very thick and show a distinct striation (Fig. 1 01). By the formation of the stomata the green assimi¬ lating tissue of the apophysis and central part of the capsule are put into direct communication with the external atmosphere. The lower part of the seta grows downward and penetrates the top of the stem of the gametophyte, from which, of course, it derives a portion of its sustenance. The centre of the seta is traversed, by a well-marked central cylinder, whose inner cells are small and thin-walled, and are mainly concerned in conducting water ; immediately outside of this is a circle of 40 ; s, seta ; a , apophysis ; sp , spores ; col, columella ; r, annulus ; o, operculum. thick-walled brown cells (Leptome of Haberlandt), and the rest of the seta is made up of nearly similar thick-walled cells which grow smaller towards the periphery. At maturity, as the supply of water is cut off from below, the capsule dries up, and all the delicate parenchyma com¬ posing the columella and inner part of the operculum, as well as that between the spore-sac and the epidermis of the theca, completely collapses, leaving little except the spores themselves, and the firm cell walls of the peristome, and the cells connecting the latter with the wall of the capsule. By the breaking down of the unthickened lateral and transverse walls of the peristomial cells, the outer and inner thickened walls are separated and 204 MOSSES AND FERNS CHAP. form the two rows of membranaceous teeth that surround the Fig. ioi. — Funaria hygrometrica (Sibth.). A, Young ; B, older stoma, from the base of the capsule ; C, vertical section, X 360. mouth of the urn (Fig. 102). By the drying up of the thin- walled cells between the annulus and the margin of the theca the operculum is loosened and is very easily separated. The Fig. io2 .-Funaria. hygrometrica (Sibth.). A, Part of the peristome ; o, an outer tooth ; i, one of the inner teeth, X85 ; B, section of the seta, X260 ; C, cross-section of upper part of calyptra, X525. teeth of the peristome are extremely hygroscopic, and probably VII THE BR YIN EH 205 assist in lifting off the operculum as well as removing the spores from the urn. When wet they bend inward, extending into the cavity of the urn. As they dry they straighten out and lift the spores out. The marked hygroscopic movements of the seta also are no doubt connected with the dissemination of the spores. The calyptra in the Bryineae is very large and is carried up on the top of the sporogonium in the form of a conspicuous membranaceous cap. As in other forms it is the venter alone that shows secondary growth. In Fu?iaria it increases very much in diameter at the base, where it is widened out like a bell, and far exceeds in diameter the enclosed embryo. Above it is narrow and lies close to the embryo. After a time the embryo grows more rapidly in length than the calyptra, which then is torn away by a circular rent about its base, and is raised on top of the elongating sporogonium. The lower portion remains delicate and nearly colourless, but the upper part has its cells thick-walled and dark brown in colour (Fig. 102, C). Tipping the whole is the persistent dark brown neck of the archegonium. Classification of the Bryinece The simplest of the Bryineae are the cleistocarpous forms or those in which there is no operculum developed, and in consequence the capsule opens irregularly. If Archidium is removed from this group the simplest form known is Ephemerum. Here, from a highly-developed filamentous pio- tonema, are produced the extremely reduced gametophores. According to Muller,1 who has studied the life-history of this genus, both male and female branches arise from the same protonema, and are only distinguishable by the smaller size of the former. The axis of the branch is scarcely at all elongated, and the leaves therefore appear close together. The sexual organs correspond closely in origin and structure to the other Bryineae. The development of the sporogonium in its early phases is also the same, and the differences only appear at a late stage. The separation of endothecium and amphithecium is apparently exactly the same as in other Bryineae, and from the former is derived the archesporium, 1 Muller (2). B. A. Fig. 103. — A, Longitudinal section of the young sporogonium of Pleuridium subulatum , X80; B, part of the same, X 600 ; archesporium ; C, young embryo of Phascum cuspidatum , optical section, X 175 ; D, cross-section of an older embryo of the same, X 350 ; sp> archesporium ; E, longi¬ tudinal section of the central part of the young sporogonium of Ephemerum phascoidcs , X350; sp, archesporium. C, D, after Kienitz-Gerloff ; E, after Muller. CHAP. VII the bryineh: 207 which like that of Funaria has the form of a hollow cylinder through which the columella passes. Between the outer spore-sac and the wall of the sporogonium an intercellular space is also formed, but the separation of the cells is complete, and there are no filaments connecting the spore-sac and the sporogonium wall as in Funaria. The cells of the archesporium are few in number and correspondingly large (Fig. 103, E), and before the division into the spores takes place all the central tissue of the columella is absorbed, and the spore mother cells occupy the whole central space. Here the division of the spores is completed, and at maturity the whole of the capsule is filled with the large spores, and no trace of the columella remains. The highest members of the Cleistocarpse, such as Phascum and Pleuridium (Fig. 104), approach very closely in structure the stego- carpous Bryineae. In these the gametophore is much better devel¬ oped than in Ephemerum , and the protonema not so conspicuous. The leaves also frequently have a well- developed midrib which is wanting in the leaves of Ephemerum. Kienitz - Gerloff 1 has carefully studied the embryogeny of Phascum cuspidatum , and except in a few minor details it corresponds very closely to that of Funaria , ex¬ cept, of course, as regards the operculum and peristome, which are absent. In Phascum , however, the archesporium is differen¬ tiated earlier than in Funaria. In each of the four primary cells of the endothecium, as seen in transverse section, a periclinal wall arises which at once separates the archesporium from the columella (Fig. 103, D). The outer spore-sac has but two layers of cells, and the capsule wall three, and between them the laree lacuna is formed as in Funaria ; but in Phascum as o in Ephemerum, the separation of the cells is complete. In the seta a slightly-developed central cylinder of conducting tissue is developed, derived, as in Funaria , from the endothecium, 1 Kienitz-Gerloff (2). 2o8 MOSSES AND FERNS CHAP. but in P has cum it is much less conspicuous. Pleuridiurn (Fig. 103, A) in its later stages corresponds exactly to P has cum , except that the capsule is more slender. In both of these o-enera the seta remains short, but is perfectly evident. fc> m Whether the absence of a distinct operculum in the cleisto- carpous Mosses is a primitive condition, or whether they are reduced forms, it is impossible to determine positively from a study of their embryogeny. Bryinece St ego carp ce Very much the larger number of Mosses belong to this group, which is primarily distinguished from the foregoing by the presence of an operculum. Of course among the 7000 or more species belonging here there are many differences in structure ; but these are mainly of minor importance morpho¬ logically, and only the more important differences can be con¬ sidered here. As we have already seen, there is great uniformity in the growth of the stem, which, with the single exception of Fissidens, has always a three-sided pyramidal apical cell. In Fissidens this is replaced by a two-sided one, but even here it has been found 1 that the underground stems have a three-sided initial cell, which is gradually replaced by the two-sided one after the apex of the shoot appears above ground. In Fissidens the leaves are arranged in two rows corresponding to the two sets of segments, and are sharply folded, so that the margins of the leaf are covered over by those of the next older ones, leaving only the apex free. A similar arrangement is found in the genus Bryosiphion ( Eustichia ), but here there is a three-sided apical cell, and the two-ranked arrangement of the leaves is secondary. The curious genus Schistostega shows also a two- ranked arrangement of the leaves of the sterile branches, but here they are placed vertically and the bases connivent, so that the effect of the whole is that of a pinnatifid leaf. The fertile branches, however, have the leaves spirally arranged, and in the sterile ones the three-sided apical cell is found. The leaves, with few exceptions, eg. Leucobryum , Fontinalis , have a well- marked midrib, and the lamina is single-layered. Leucobryum (Fig. 107, A) has leaves destitute of a midrib, and made up of 1 Goebel (8), p. 371. VII THE BR YIN EHZ 209 two or three layers of cells, large hyaline ones, somewhat as in Sphagnum , and small green cells. The hyaline cells, as in Sphagnum , have round holes in the walls, but no thickenings. The midrib may be narrow, as in F unaria , or it may occupy nearly the whole breadth of the leaf, as in the Polytrichaceae, where, owing to the almost complete suppression of the lamina, secondary vertical plates of green cells are formed (Fig. 107, B). The one-third divergence of the leaves found in Fontinalis 1 is replaced in most other genera by a larger divergence.2 Thus in Funaria hygrometrica it is -| ; in P oly trichum commune yk ; in P. formosum As the archegonia are borne upon lateral branches, or upon the main axis, the stegocarpous Bryineae are frequently divided into two main divisions, the Pleurocarpae and the Acrocarpae, which are in turn divided into a number of subdivisions or families. How far the division into acrocarpous and pleuro- carpous forms is a natural one may be doubted, as probably the latter is secondary, and it is quite conceivable that different families of pleurocarpous forms may have originated inde¬ pendently from acrocarpous ones. The simplest of the stegocarpous Mosses, while having the operculum well marked, have no peristome. Thus the genus Gymnostomum has no peristome at all, and in an allied genus, Hymenostomum , it is represented by a thin membrane covering the top of the columella. In nearly related genera, however, eg. IVeisia, a genuine peristome is present. The Tetraphideae, represented by the genus Tetraphis (Fig. 105), are interesting as showing the possible origin of the peristome, as well as some other interesting points of structure. Tetraphis pellucida is a small Moss, which at the apex of its vegetative branches bears peculiar receptacles containing multi¬ cellular gemmae of a very characteristic form. The leaves that form the receptacle are smaller than the stem leaves, and closely set so as to form a sort of cup, in which the gemmae are produced in large numbers. These arise as slender multi¬ cellular hairs, the end cell of which enlarges and forms a disc, at first one-layered, but later, by walls parallel to the broad surfaces, becoming thicker in the middle, and lenticular in form. The arrangement of the cells in the young gemmae looks as if 1 This seems to be strictly the case only in the smaller branches ; in the larger axes the leaves are not exactly in three rows. 2 Goebel (8). P 210 MOSSES AND FERNS CHAP. the growth of the bud was due to a two-sided apical cell (Fig. 105, C), but this point was not positively determined. These gemmae give rise to a protonema of a peculiar form, from which in the usual way the leafy stems develop. The protonemal filaments grow into flat thalloid expansions that recall those of Sphagnum and Andrecea. The sporogonium of Tetraphis has a peristome of peculiar structure, and not strictly comparable to that of any of the Fig. i°S' Tetraphis pellucida (Hedw.). A, Plant \v4th gemmte, x6; B, upper part of the same, *5°> C, young gemma, X600; D, a fully-developed gemma, X300. other Mosses. After the operculum falls off the tissue lying beneath splits into four pointed teeth, which, however, are not, as in Funaria, composed simply of the cell walls, but are masses of tissue. All of the other higher Bryineae, with the exception of the Polytrichaceae, have the peristome of essentially the same struc- tuie as that described for Funaria. Sometimes the teeth do not separate but remain as a continuous membrane, i.e. the inner peiistome of Buxbaumia, or a perforated membrane, as in Fontinalis (Fig. 106, B). VII THE BRYINExE 21 I The base of the capsule, or apophysis, which Haberlandt 1 Fig. 106. — \,Splachnuinamptillaceum(X,.), longitudinal section of the sporogonium (after Haberlandt) ; a, apophysis ; c, capsule ; B, peristome of Fontinalis antipyretica (L.) ; C, peristome'.of A trichum iindulatum (after Schimper) ; D, sporogonium of Polytrichum commune (L.); i, with the calyptra ; 2, with the calyptra removed ; E, Buxbaumia , X 4. has shown to be the principal assimilative part of the sporo- 1 Haberlandt (4). 212 MOSSES AND FERNS CHAP. gonium, and which alone is provided with stomata, sometimes becomes very large, and in the genus Splachnum 1 especially forms a largely -developed expanded body, which must be looked upon as a specially-developed assimilating apparatus (Fig. 106, A). Undoubtedly the Polytrichacese represent the highest stage of development among the Musci. This is true both in regard to the gametophore and the sporogonium. The former reaches in some species, i.e. P. commune , a length of 20 centimetres and sometimes more. The stem is usually angular and the closely-set leaves thick and rigid. The numerous rhizoids are often closely twisted together and form cable-like strands. The structure of the leaves is very characteristic, and differs very much from that of the simpler type found in Funaria. In Polytrichum (Fig. 107, B) the midrib is very broad, and only at the extreme margins of the leaf is the lamina one-layered. Seen in cross-section 2 the leaf appears somewhat crescent¬ shaped. The cells of the margin of the section, and also a line of cells running through the central part, are comparatively thin- walled, and the latter are empty water-conducting cells similar to the tracheae in the vascular bundles of the higher plants. Next to these cells on the lower side of the leaf are a number of similar but somewhat smaller cells containing starch, and the rest of the section is made up principally of very thick-walled sclerenchyma. The outer cells contain more or less chloro¬ phyll, but the principal assimilative tissue consists of a series of vertical cell plates or laminae parallel to the long axis of the leaf, and seen in cross-section appear as short vertical rows of four or five cells. These cells contain numerous chloroplasts, and the laminae cover the whole upper surface of the leaf except the extreme margin and the sheathing part of the base, where they are wanting. The structure of the stem of P. commune is thus described by Goebel.3 “ A transverse section of the stem shows the following structure. In the centre is a cylinder of broad thick- walled cells, with here and there those whose walls have remained thin. The thickened walls show a yellowish colour. Surround¬ ing this cylinder is a ring of several layers of thin-walled narrow cells, which is bounded on the outside by from one to three layers of cells with thin, mostly very dark brown walls. These 1 Vaizy (3). 2 strasburger (10). 3 Goebel (8), p. 369. VII THE BR YINEsE 213 latter, as well as the are characterised by the starch contained in them, as are the narrow cells of the leaf - traces. Other¬ wise starch is often com¬ pletely absent from the stem of Polytrichum and is replaced by oil. The latter is abundant, and probably albuminoids as well, in the thin -walled tissue surrounding the central cylinder. In the latter oil is not so abund¬ ant, as its cells for the most part contain only air.” The leaf - traces, or continuation of the central tissue of the midribs of the leaves, bend down into the stem, and fin¬ ally unite with the axial cylinder of the latter, in a manner quite analogous to that found in the stems of many vascular plants. Bastit,1 who more re¬ cently has made a com¬ parative study of the subterranean and aerial stems of P. juniperinum, divides the outer tissue of the latter into epi¬ dermis, hypoderma, and cortex. In the subter¬ ranean stems he finds the construction quite differ¬ ent from that of the leafy cells lying immediately within, Fig. 107 . — A, Transverse section of the leaf of Leitco- bry-um ; B, similar section of the leaf of Polytrichum commune ; cl, chlorophyll-bearing cells (after Goebel). 1 Bastit (1), p. 295. 214 MOSSES AND FERNS CHAP. branches. The section of the former is triangular, and its epi¬ dermis provided with hairs which are absent from the epidermis of the aerial parts. Rudimentary scales, arranged in three rows, are present, and corresponding to these are strands of tissue that represent the leaf-traces of the aerial stems. The central cylinder is much larger relatively than in the leafy branches, and its cross-section is not continuous, but is interrupted by three “ pericyclic sectors,” composed of cells whose walls are but little thickened. The point of each sector is at the peri¬ phery of the medulla, or central cylinder, and the broad end toward the centre. As might be expected, intermediate con¬ ditions are found where the rhizome begins to grow upward to form a leafy branch. The male inflorescence of the Polytrichaceae is especially conspicuous, as the leaves immediately surrounding the anther- idia are different both in form and colour from those of the stem. They are broad and membranaceous, and more or less distinctly reddish in colour. A well-known peculiarity of these forms is the fact that the growth of the stem is not stopped by the formation of antheridia, but after the latter have all been formed the axis resumes its growth and assumes the character of an ordinary leafy branch. This, of course, indicates that, unlike most of the Mosses, the apical cell does not become transformed into an antheridium, and the researches of Hof- meister,1 Leitgeb,” and Goebel 3 have shown that this is the case. The antheridia form groups at the base of each leaf of the inflorescence, and Leitgeb thinks it probable that each group represents a branch, i.e. the inflorescence is a compound structure, and not directly comparable to the simple male inflorescence of Funaria. The sporogonium in Polytrichum has a large intercellular space between the inner spore-sac and columella as well as the one outside the outer spore-sac. In both cases the space is traversed by the conferva -like green filaments found in the other stegocarpous Mosses. The apo¬ physis is well developed, especially in Polytrichum , and the calyptra very large and covered with a dense growth of hairs (Fig. 106, D). The structure of the peristome in the Polytrichaceae is entirely different from that of the other Mosses. It is com¬ posed of bundles of thickened fibrous cells arranged in crescent 1 Hofmeister (2). 2 Leitgeb (9). s Goebel (7). VII THE BR YINEsE 215 form, the ends of the crescent pointing up, and united with the adjacent end of the bundle next it. The tops of the teeth thus formed are connected by a layer of cells stretching across the opening like the head of a drum. This membrane is known technically as the “ Epiphragm ” (Fig. 1 06, C). The Buxbaumiacece The last group of Mosses to be considered is the very peculiar one of the Buxbaumiaceae. In these Mosses the gametophyte is extraordinarily reduced, although the sporo- gonium is large and well developed. So simple is the sexual plant, that Goebel 1 has concluded that these ought to be taken away from the rest of the Mosses, and removed to a distinct order. According to Goebel’s account, the antheridia, which are long stalked, are borne directly upon the protonema, and subtended by a single colourless bract. The female branches are also very rudimentary, but less so than the male. On the strength of the extreme simplicity of these, Goebel thinks that Buxbaumia is a primitive form allied to some alga-like progenitor of the Mosses. There are, however, two very strong objections to this. First the sporogonium, which is extremely large, and complicated in structure, and essentially like that of the other stegocarpous Mosses ; secondly, Buxbaumia has been shown by Haberlandt2 to be distinctly suprophytic in its habits, and the extreme reduction of the assimilative tissue of the gametophyte is quite readily explicable from this cause. Fossil Muscinece The remains of Muscineae in a fossil condition are exceed¬ ingly scanty ; so much so indeed as to practically throw no light upon the question of their origin and affinities, as nearly all of the forms discovered belong to the later formations, and aic either indentical with living species or closely allied forms. No doubt the great delicacy of the tissues of most of them, especially the Hepaticae, accounts in great measure for their absence from the earlier geological formations. 2 Haberlandt (4), p. 480. 1 Goebel (16). 2l6 MOSSES AND FERNS CHAP. The A ffinities of the Musa It is perfectly evident that the Mosses as a whole form a very clearly defined class, and that their relationship with other forms is at best a somewhat remote one. Sphagnum, however, certainly shows significant peculiarities that point to a connection between this genus, at least, and the Hepaticae. It will be remembered that the protonema of SpJiagnum is a large flat thallus, and not filamentous, as in most Bryineae. It is noteworthy, however, that from the margin of this flat thallus later filamentous branches grow out which are apparently identical in structure with the ordinary protonemal filaments of the Bryineae. In Andrecea similar flat thalloid protonemata occur, but not so largely developed as in Sphagnum , and finally in Tetraphis a similar condition of affairs is met with. As this occurs only among the lower members of the Moss series, the question naturally arises, does this have any phylogenetic meaning ? While it is impossible to answer this question positively, it at any rate seems probable that it has a significance, and means that the protonema has been derived from a thalloid form related to some thallose Liverwort, and that by the suppression of the thalloid portion, as the leafy gametophore became more and more prominent, the filament¬ ous branches, which at first were mere appendages of the thallus, finally came to be all that was left of it. The view of Goebel and others that the filamentous form of the protonema is the primitive one, and indicates an origin from alga-like forms, might be maintained if the question were concerned simply with the protonema ; but when the structure of the sexual organs, especially the archegonium, is considered, and the development of the sporophyte, the difficulty of homologising these with the corresponding parts in any known Alga is apparent, while on the other hand the resemblance between them and those of the Hepaticae is obvious. As to which group of the Hepaticae comes the nearest to the Mosses, the answer is not doubtful. The remarkable similarity in the development and structure of the sporogonium of Sphagnum and the Anthoceroteae, leaves no room for doubt that as far as Sphagnum is concerned, the latter come nearest among existing forms to the ancestors of Sphagnum. Of VII THE BR YIN EH 21 7 course this does not assume a direct connection between Sphagnum and any known form among the Anthoceroteae. There are too many essential differences between the two to allow any such assumption : but that the two groups have come from a common stock seems reasonably certain, and the structure of the capsule in Sphagnum points to some form which like Anthoceros had a highly -developed assimilative system. This is indicated by the presence of stomata, which, although functionless, probably were once perfect, and make it likely that with the great increase in the development of the gametophyte the sporophyte has lost to some extent its assimilative functions, which have been assumed by the gametophyte. Andrecza, both in regard to the gametophyte and the sporo¬ phyte, is in many ways intermediate between Sphagnum and the other Mosses. The resemblance in the dehiscence of the sporogonium to that of the Jungermanniaceae is probably accidental. It may perhaps be equally well compared to the splitting of the upper part of the capsule into four parts, in Tetraphis , although in the latter it is the inner tissue and not the epidermis which is thus divided. If this latter suggestion proves to be true, then there would be a direct connection of Andrecza with the stegocarpous Bryineae, and not through the cleistocarpous forms. These latter would then all have to be considered as degraded forms derived from a stegocarpous type, unless, with Leitgeb, we consider them as a distinct line of development leading up to the higher Bryineae, entirely independent of the Sphagnaceae, and with Archidium and Ephemerum as the simplest forms. His comparison of these forms with Notothylas , however, cannot be maintained with our present knowledge of that genus, and more evidence is needed before his view can be accepted ; but the possibility of some such explanation of the cleistocarpous Bryineae must be borne in mind in trying to assign them their place in the system. The objections to considering Buxbaumia a primitive form have been already given, and it is not necessary to repeat them. CHAPTER VIII THE PTERIDOPHYTA- — OPHIOGLOSSACE^E In tracing the evolution of the Bryophytes from the lowest to the highest types the gradual increase in the importance of the second generation, the sporophyte, is very manifest. This may or may not be accompanied by a corresponding develop¬ ment of the gametophyte. In the line of development represented by the higher Mosses, in a general way the two have been parallel, and the most highly differentiated gametophyte bears the most complicated sporophyte, as may be seen in Polytrichum , for example ; but in the Hepaticse this is not the case, and much the most highly organised sporophyte here, that of Authoceros, is produced by a very simple game¬ tophyte. In this evolution of the sporophyte, it approaches a condition where it is self-supporting, but in no case does it become absolutely so. A special assimilative tissue, it is true, is developed, and in some of the true Mosses, such as Splachnum, this goes so far that a special organ, the apophysis, is formed ; but, as we have seen, the sporogonium is dependent for its supply of water and nitrogenous food upon the gametophyte, with which it remains intimately associated, and upon which it lives as a parasite. In the Pteridophytes the case is different; here by the development of a special organ, the root, the young sporophyte is brought into direct communication with the source of supply of water, and the food materials dissolved in it. In the few cases where true roots are absent their place is taken by other structures that perform their functions. The assimilative activity is restricted to special organs, the leaves, except in a few cases ch. viii THE PTERIDOPH YTA—OPHIOGLOSSA CEzE 219 where these become much reduced, as in Psilotum or Equisetum. A main axis is present upon which the leaves are borne as appendages, and which continues to form new leaves and roots as long as the sporophyte lives. The differentiation of these special organs begins while the sporophyte is still very young. The earliest divisions in the embryo correspond closely to those in the embryo of a Bryo- phyte, but instead of forming simply a capsule, as in all the Bryophytes, there is established more than one growing point, each one forming a distinct organ. In the Ferns there are four of these primary growing points, giving rise respectively to the stem, leaf, root, and foot. The latter is a temporary structure, by which the young sporophyte absorbs food from the gametophyte, but as soon as it becomes independent this gradually withers away, and soon all trace of it is lost. The originally homogeneous tissues of the embryo become differentiated into the extremely complicated and varied tissues characterising the mature sporophyte. The most characteristic of these are the vascular system of tissues. This is hinted at in the central strand of tissue in the seta of many Mosses, and the columella of the Anthoceroteae ; but in no Bryophyte does it reach the perfect development found in the Ferns and their relations, which are often called on this account the vascular cryptogams. The gradual reduction in the vegetative parts of the gametophyte, from the large long-lived prothallium of the Marattiaceae to the excessively reduced one found in the heterosporous Pteridophytes, has already been referred to in the introductory chapter. The structure of the sexual organs of the Pteridophytes appears at first sight radically different from that of the Bryophytes, but a careful comparison of the lower forms of the former with some of the Hepaticae, especially the Anthoceroteae, shows that the difference is not so great as it at first sight appears. A further discussion of this point must be left, how¬ ever, until we have considered more in detail the structure of these parts in the different groups of the Pteridophytes, where they are remarkably uniform. In all of them the archegonium has a neck composed of but four rows of peripheral cells, instead of five or six, as in the Bryophytes, and the antheridium, except in the leptosporangiate Ferns, is more or less completely sunk 220 MOSSES AND FERNS CHAP. in the tissue of the prothallium. The spermatozoids are either biciliate, as in Mosses, or multiciliate, a condition which, so far as is known, does not exist among the Bryophytes. The formation of spores is very much more subordinated to the vegetative life of the sporophyte than is the case among the most highly organised of the Bryophytes. Indeed it may be many years before any signs of spore formation can be seen. The spores are always born in special organs, sporangia, which are for the most part outgrowths of the leaves, but may in a few cases develop from the stem. In the simplest cases the spores arise from a group of hypodermal cells, generally trace¬ able to a single primary cell. The cell outside of these divides to form a several-layered wall, but the limits of the sporangium are not definite, and it may scarcely project at all above the general surface of the leaf. From this condition found in Ophioglossum , there is a complete series of forms leading to the so-called leptosporangiate type, where the whole sporangium is directly traceable to a single epidermal cell, and where a very regular series of divisions takes place before the archesporium is finally formed. With very few exceptions all of the existing Pteridophytes fall naturally into three series or classes of very unequal size. The first of these, the Ferns or Filicineae, is the predominant one at present, and includes at least nine-tenths of all living Pteridophytes. The Equisetineae are the most poorly repre¬ sented of the modern groups, and include but a single genus with about twenty-five species. The third class, the Lyco- podineae, is much richer both in genera and species than the Equisetineae, but much inferior in both to the Filicineae. The disproportion between these groups was much less marked in the earlier periods in the world’s history, as is attested by the very numerous and perfect remains of Pteridophytes occurring especially in the coal-measures. At that time both the Equisetineae and Lycopodineae were much better developed both in regard to size and numbers than they are at present. Class I. Filicinece The Filicineae, as already stated, include by far the greater number of existing Pteridophytes, and are much more ex¬ tended in range and abundant in numbers than either of the VIII THE P TEPID OP H YTA—OPHIOGLOSSA CITE 221 other classes. A marked characteristic of all Ferns is the large size of the leaves, which are also extremely complicated in form in many of them. In a few of these the leaves are simple, i.e. Ophioglossum, Vittaria, Pilularia , but more commonly they are pinnately compound and sometimes of enormous size. The stem varies a good deal in form and may be very short and completely subterranean, as in species of Ophioglossum and Botrychium, or it may be a creeping rhizome, or in some of the large tropical Ferns it is upright, and grows to a height of 8 to i o metres, or even more. While some forms of the Ferns are found adapted to almost all situations, most of them are moisture -loving plants, and reach their greatest development in the damp forests of the tropics. A few, eg. Ceratopteris, Azolla , are genuine aquatics, and still others, eg. species of Gymnogramme , live where they become absolutely dried up for several months each year. These latter will quickly revive, however, as soon as placed in water, and begin to grow at once. In the tropical and semi- tropical regions many Ferns are epiphytes, and form a most striking feature of the forest vegetation. With few exceptions the sporophyte is long-lived, but a few species are annual, eg. Pilularia Americana , Mars ilia vestita, and depend entirely upon the spores for carrying the plant through from one season to another. The sporophyte may give rise to others by simply branching in the ordinary way, or special buds may be developed either from the stem or upon the leaves ( Cystopteris bulbifera). Besides the normal production of the gametophyte from the spore, it may arise in various ways directly from the sporophyte (apospory) ; and conversely the latter may develop as a bud from the gametophyte without the intervention of the sexual organs (apogamy). The Filicineae include both eusporangiate and leptospor- angiate forms, — indeed the latter occur only here. The former comprise the homosporous orders, Ophioglossaceae and Maratti- acese, and the heterosporous order Isoetaceae, whose systematic position, however, it must be said is still doubtful. The Leptosporangiatae include the single great homosporous order Filices, and the two heterosporous families, closely related to it, the Salviniaceae and the Marsiliaceae. These are usually classed together as a distinct order, the Hydropterides or Rhizocarpeae. 222 MOSSES AND FERNS CHAP. The Homosporous Eusporangiatce The two orders, Ophioglossaceae and Marattiacese, show many evidences of being very ancient forms, and in several respects seem to approach more nearly to the Hepaticae than any other Pteridophytes. While they are different from each other in many respects, still there is sufficient evidence to indicate that they belong to a common stock to warrant placing them near each other in the system. The Ophioglossacece The gametophyte of the Ophioglossaceae is still very in¬ completely known, and only in a few forms. Mettenius 1 described the older stages of Ophioglossum pedunculoswn , and Hofmeister 2 similar prothallia of Botrychium lunaria, but they were unable, as later observers have been, to procure the earlier conditions. In both cases the prothallia were subterranean and entirely destitute of chlorophyll. In Ophioglossum, how¬ ever, when it reached the surface of the ground, the part exposed to the light became somewhat flattened and green. The earliest stages that Mettenius found consisted of a nearly globular tubercle, from which a single conical protuber¬ ance grew upward, having a branch that in extreme cases reached a length of as much as two inches (Fig. 108). This branch grows by a single apical cell, and may occasionally branch dichotomously, and always grows towards the light. On reaching the surface of the ground the growth is checked and a flattened expansion is produced whose cells contain chlorophyll. The sexual organs are borne almost exclusively upon the subterranean parts of the branch, and in great numbers. On the weaker prothallia antheridia prevail, on the stronger ones archegonia. The structure and development of these correspond closely with those of the other eusporangiate Pteridophytes. The antheridia are completely sunk in the tissue of the prothallium, and the outer wall is composed of two layers of cells (Fig. 108, C). The archegonia have a short neck, which projects but little above the surface. The number of canal cells does not seem to have been determined (Fig. 108, D). 1 Mettenius (3), p. 119. 2 Hofmeister (1), p. 307. VIII THE P TERIDOPH ] 'TA—OPHIOGLOSSA CE.E The prothallium of Botrychium lunaria 1 is much smaller and does not grow to the surface of the ground. It is oval in form, and consists of a mass of firm tissue, brownish towards the outside and colourless within, where the cells are also larger. Scattered root-hairs grow from the superficial cells, and the prothallia are monoecious. The antheridia, which correspond c D Fig. 108 .—Ophioglossum fedunculosum (Desv.). A, B, Prothallia, X 2 ; T, the primary tubercle; C, antheridium, X200 ; D archegonium ; E, a young embryo (after Mettenius). closely to those of Ophioglossum, are produced principally upon the upper surface, the archegonia below. The latter correspond in structure to those of Ophioglossum , but to judge from Hofmeister’s figure the neck is somewhat longer and projects 1 Hofmeister, l.c. 224 MOSSES AND FERNS CHAP. more above the surface. The spermatozoids are described as similar to those of the Polypodiaceae, but half as large again. The writer has succeeded in securing the earliest phases of germination in two other species, viz. Ophioglossum ( Ophioderma ) pendulum and Botrychium Virginianum , as well as the older prothallia of the latter. The germination in both cases is extremely slow, especially in the former, where a year and a half after the spores were sown the largest prothallia had but three cells. Probably under natural con¬ ditions the growth is more rapid. The spores of both forms show much the same structure. The tetrahedral spores contain granular matter, with numerous oil -drops, and a central large and distinct nucleus. The exospore is colourless, and upon the outside presents a pitted appearance in Ophioglossum , and irregular small tubercles in Botrychium. The perinium or epispore is not clearly distinguishable from the exospore. In both cases chlorophyll is absent in the ripe spore. The first sign of germination is the absorption of water and splitting of the exospore along the three radiating lines on the ventral surface of the spore. The spore enlarges considerably before any divisions occur, but remains globular in form, and no chlorophyll can be detected. In this condition, which was observed within two weeks after the spores were sown in Ophioglossum , it may remain for several months unchanged. The first division wall is usually at right angles to the axis of the spore, and divides it into two nearly equal cells, of which the lower has more of the granular contents than the upper one. The endospore is noticeably thickened where it protrudes through the ruptured exospore. The next wall, in all cases observed, is at right angles to the first, and always in the lower cell, which it divides into equal parts (Figs. 109, no). In Botrychium at this stage a few large chloroplasts were seen in both upper and lower cells, but Ophioglossum showed no positive evidence of chlorophyll, although it seemed sometimes as if a faint trace of chlorophyll Fig. 109. — Germinating spore of Ophioglossum ( Ophio - derma) pendulum (L.). A, Surface view ; B, optical section, X 600. VIII THE PTERIDOPH YTA — OPHIOGLOSSACE.E 225 could be detected. As growth proceeds, the oil partially disappears, and the cells become much more transparent than at first. Up to the present writing no further observations have been made, but it is hoped later that some additional informa¬ tion may be obtained on this important point. In July 1893, at Grosse lie, Michigan, the writer was fortunate enough to find a number of old prothallia of Botrych- tum l irginianum. They were all connected with the young sporophyte, and were too old for studying at all completely the Fig. iio. — Botrychium V irginianum (Sw.). A, B, Germinating spore, X600; C prothallium (/r), with young sporophyte attached, X2 ; D, longitudinal section of the prothallium, showing the foot of the embryo (/), X4 ; E, first (?) leaf of a young sporophyte, X2. development of the sexual organs and embryo. They resembled closely those of B. lunaria, but were very much larger. They grew at a distance of several centimetres beneath the surface of the ground, in the neighbourhood of a number of large speci¬ mens of the mature plant. The prothallium at this stage, like that of B. lunaria , is completely destitute of chlorophyll, and has the form of a slightly flattened tuber, which in the larger ones showed fold -like ridges upon' the upper surface. The outer cells were brownish, and short root-hairs grew in large Q 226 MOSSES AND FERNS CHAP. numbers from these. The inner tissue was colourless and large-celled, and in the cells of the lower part of this tissue were observed in all cases great numbers of irregular colourless filaments that had all the appearance of an endophytic fungus. Whether this is of the nature of a mycorrhiza remains to be seen, but it is by no means impossible that such should be the case. This lower tissue forms a distinct zone, which in section appears much more opaque than the upper zone, from whose outer cells the sexual organs arise. The sexual organs were found as a rule only upon the upper side, in which respect it differs from B. lunaria, where the archegonia usually are formed on the lower side. The material was too old to make it possible to tell whether the growth of the prothallium was from a single apical cell or not. All of the archegonia found were old, and it was im¬ possible to follow their development, and the details of the structure of the .ripe archegonium could not be made out. A striking point of difference between it and the other forms hitherto investigated is the long neck, which projects quite as much above the prothallium as that of the leptosporan- giate Ferns (Fig. in, C). In general appearance it closely resembles that of Osmunda , being straight and not curved backward, as in most Ferns. The antheridia may either occur singly, in which case they are sunk in the thallus, or sometimes groups of them occur together upon short branches projecting from the upper surface. In the latter condition the individual antheridia often project somewhat. So far as could be judged from a study of a very small number of young stages, the development corresponds exactly to that in Equisetum or Marattia. The antheridium mother cell probably, as in these, divides fiist by a wall parallel to its outer surface into two cells, and the inner one divides next by alternate trans¬ verse and vertical walls into the mass of sperm cells. In some cases the outer cell divides both by vertical and transverse walls, so that the outer wall of the ripe antheridium is two¬ layered, as in B. lunaria ; but quite as often it remains but one cell thick (Fig. ill, B), in which respect it resembles Equisetum or Marattia. The spermatozoids were not observed. In only one case was a young embryo found, and this, so fai as could be determined, also resembled in the arrangement of its cells the similar condition in Marattia , but the prepara- VIII THE PTE RID OP H YTA — OPHIO GLOSS A CE.E 227 tion was not a satisfactory one, and the results not conclusive. Although the young plants were so far advanced (Fig. 1 10) it was a significant fact that the prothallium still remained alive. A section through the base of the young sporophyte showed the foot, which is extraordinarily large here, and a microscopic examination showed that the peripheral cells of the foot were full of protoplasm, and their nuclei extremely distinct, and the cells were evidently still actively engaged in absorbing food Fig. hi .—Botrychium Viginianum (Svv.). A, Young; B, older anLheridium, longitudinal sections. A, X600; B, X300; C, section of old archegonium, X300. from the prothallium for the support of the sporophyte. The single leaf in these young plants was not probably the coty¬ ledon, which had apparently disappeared, and is probably of simpler structure. Hofmeister found that in B. lunaria the first two roots were formed before the first green leaf, and that the first three leaves are scale-like. The fourth leaf is the first to appear above the ground, which it only does the second year, or possibly later. The position of the archegonium in this species 228 MOSSES AND FERNS CHAP. VIII upon the lower surface, necessitates a bending upward of the growing point of the young sporophyte, which is not the case in B. Virginianum , where the archegonium is above, and the sporophyte grows up vertically from the beginning. Mettenius’ account of the development of the embryo in 0. pedunculosuin is somewhat more complete. The earliest stage seen by him was already multicellular, and the young embryo had the form of an oval cell mass in which the primary divisions were not recognisable (Fig. 108, E). The upper part, i.e. that next the archegonium neck, grows up at once into the cotyledon, while the opposite part gives rise to the first root. These grow respectively upward and downward, and break through the overlying prothallial cells. Later, at a point between the two, the stem apex is developed. The first leaf here becomes green, and develops a lamina similar to that of the later-formed ones. Usually but one embryo is developed from the prothallium, but occasionally two are formed, especi¬ ally where the prothallium forks. Ophioglossum (Ophioderma) pendulum, an epiphyte common in the Eastern tropics, may be taken as a type of the simplest of the Ophioglossaceae. Its short creeping stem grows upon the trunks of trees, especially tree-ferns, from which the long flaccid leaves hang down. The lamina of the leaf merges insensibly into the stout petiole whose fleshy base forms a sheath about the next younger leaf. Corresponding to each leaf is a thick unbranched root, which penetrates into the crevices of the bark and holds the plant secure. These roots are smooth, and show no trace of rhizoids. The petiole is continued up into the lamina as a very broad and thick midrib, which in the sporiferous leaves (sporophylls) is continued into the peculiar elongated spike which bears the sporangia. The petiole if cut across shows a number of vascular bundles arranged in a single row, nearly concentric with the periphery of the section. As these enter the lamina they anastomose and form a network with elongated meshes (Fig. i 14, C) and no free ends. Sections of the spike cut parallel to its broad diameter show a somewhat similar arrangement of the vascular bundles, but here there are free branches extending between the sporangia. The relations of the bundles of the fertile and sterile parts of the leaf are best followed in the FiG. 112 .—Ophioglossum pendulum (L.)- A, Leaf with sporangiophore, natural size; B, cross- section of the petiole, x6 ; C, section of the sporangiophore, parallel to its broad surface X6. 230 MOSSES AND FERNS CHAP. smaller species. Prantl 1 describes it as follows for O. Lusitani- cuin , and states that it is essentially the same in other species. “ The primary bundle given off from the stem branches just after it enters the petiole. The main bundle gives off two smaller lateral branches right and left. The latter branch again near the base of the spor- angiophore, and the upper branches from each unite to form the single bundle that enters the latter.” The sporangia are large cavities sunk in the tissue of the sporophyll, and scarcely projecting at all above the surface, where the position of each one is indicated by a faint transverse furrow which marks the place where it opens. Seen in sections parallel to the flat surface these appear per¬ fectly round, but in trans¬ verse section are kidney¬ shaped (Fig. i 2 i, C). The apex of the stem forms a blunt cone, which, however, is not visible from the outside. A longitudinal section through the end of the stem shows that it is covered by a sheath com¬ posed of several layers of cells, and this encloses a cavity in which are the growing point of the stem and the youngest leaf. The leaves here form much more rapidly than 1 Prantl (7), p. 155. Fig. 113. — Ophioglossum vulgatum (L.), Xi. VIII THE P TER1D0PH I 'TA — OP H 10 GL OSSA CEAZ 231 in the species of the temperate regions, as the growth continues uninterruptedly throughout the year. The real apex of the stem forms an inclined nearly plane surface, slightly raised in the centre, where the single apical cell is placed (Fig. 1 15, A, B). This cell is by no means conspicuous, and not always readily found, but probably is always present. It has the form of an inverted three-sided pyramid, but the lateral faces are more or less strongly convex, and the apex may be trun¬ cate. From the few cases observed it is not possible to say whether in addition to the three sets of lateral segments basal segments are also formed, but it is by no means impossible that such is the case. According to recent investigations of Rostowzew1 the apical cell of the stem of Ophioglossum vulgatum shows consider- able variation, and may be either a three or four-sided prism, i.e. it apparently also may have the base truncate. Holle’s 2 description agrees with this except that he states that he always found the cell pointed below, not truncate. The segments cut off from the lateral faces are large, and the divisions irregular. They are apparently formed in very slow succession, and the irregularity of the succeeding divisions in the segments themselves soon makes it impossible to trace their limits. Each segment apparently gives rise to a leaf, but this is impossible to determine with certainty. The first wall in the young segment probably divides it into an inner and outer cell, but the next divisions could not be deter¬ mined positively. Probably, as in Botrychium , the outer cell is 1 Rostowzew ( 1 ), p. 451- " Hollo (1). A. C longitudinal section of stem apex, X4 ; x, the growing point; B, young sporophyll, X2; sp , the sporangiophore ; C, an older leaf, showing the venation, X 2. 232 MOSSES AND FERNS CHAP. next divided by a vertical wall, perpendicular to the broad faces of the segment, into two cells, in which divisions then take place in both transverse and longitudinal direction without strict regularity. The stem is mostly made up of thin-walled parenchyma, and the vascular bundles are much less developed than is the case in the underground stem of 0. vulgatum or Botrychium. The bundles are of the collateral form, i.e. the inner side is occupied by the xylem, the outer by the phloem, and there is no bundle-sheath developed. The bundles form a very irregular wide-meshed cylinder, not differing essentially from that in 0. vulgatum. The young leaf is completely concealed by the sheath formed by the base of the next older one. It is at first a conical protuberance arising close to the stem apex, around which its base gradually grows and forms the sheath about it and the next leaf rudiment. It is probable that here, as in O. vulgatum } the young leaf grows at first by a definite apical 1 Rostowzew (i). p. 451. VIII THE P TER ID OP H YTA — OP H 10 GLOSS A CITE cell. After the plant has reached a certain age, each leaf gives rise to a sporangial spike, which becomes evident while the leaf is still very small. The first indication of this is a conical outgrowth upon the inner surface of the leaf, about halfway between the apex and base. A longitudinal section of this shows it to be made up of large cells, especially toward the top ; but although there was sometimes an appearance that indicated the presence of a single apical cell, this was by no means certain, and if there is such an initial cell, its divisions must be very irregular. The subsequent growth of the leaf is for a long time mainly from the base, and the young sporangial spike is much nearer the apex in the next stage (Fig. i 14, B). No distinct petiole has yet developed, but the centre of the young leaf, up to the point of attachment of the spike, is traversed by the thick mid¬ rib, above which the lamina is still very small. The young spike now forms a beak-shaped body curving inward and up¬ ward, and sections of slightly older stages than the one figured show the first indications of the developing sporangia. Later still the base of the leaf becomes narrowed into the petiole, and the spike also becomes divided into the uppei sporiferous portion and the short slender pedicel. The anatomical structure of the leaf is extremely simple. The epidermis is composed of rather thick-walled cells, irregulaily polygonal in outline, with large stomata at intervals, about which the cells are arranged concentrically, and frequently with a good deal of regularity. The stomata themselves (Fig. 1 1 6), seen from above, have an angular outline, but from below aie perfectly oval, and cross-sections show that this appearance is due to a partial overarching of the guard cells of the stoma by the surrounding epidermal cells. The upper walls of the guaid cells are thickened irregularly, giving them the appearance of Fig. 1 16.— Stoma from the leaf of Ophioglossum ■pendulum, X260. 234 MOSSES AND FERNS CHAP. being folded longitudinally. There is no distinct hypoderma formed, and the bulk of the leaf is made up of a uniform meso- phyll composed of nearly globular cells with much chlorophyll, and separated by numerous intercellular spaces. In the petiole the tissues are similar, but more compact, and the walls of the ground tissue are all deeply pitted. The vascular bundles are nearly circular in section and show a compact mass of tracheary tissue (Fig. i 1 7, t), surrounded by nearly uniform cells with Fig. 1 17. Vascular bundle of the petiole of O. pendulum, x26o ; t , /, the xylem of the bundle. moderately thick colourless walls. The limits of the bundle are not, as in the higher Ferns, marked by a distinct bundle- sheath, but are indicated simply by the somewhat smaller size of the cells of the bundle itself — indeed it is not always easy to say exactly where the ground tissue begins. The xylem is composed of pointed tracheids whose walls are marked with thick leticulate bands. 1 his mass of tracheary tissue is situated near the inner side of the bundle, which like that of the stem is collateral. The rest of the bundle is composed of sieve-tubes VIII THE P TERIDOPH YTA — OPHIO GLOSS A CEAL 235 mingled irregularly with smaller cambiform cells. Whether or not sieve-tubes occur upon the inner side of the bundle could not be positively determined. The sporangiophore has much the same anatomical structure as the rest of the leaf, but stomata are quite absent from its epidermis. In this respect 0 . pendulum differs from O. vulgatum and allied species, where stomata are developed upon the sporangiophore as well as upon the rest of the leaf. The Root The roots are formed singly near the bases of the leaves, and are light yellowish brown in colour, and so far as could be Fig. 1 18. — Ophioglossum pendulum(X,.\ A, Longitudinal ; B, transverse sections of theroot apex, X aiS- seen, entirely unbranched. Sections show that here, as in most vascular plants, the growing point of the root is not at the apex, but some distance below and protected by the root-cap. The growth of the root in Ophioglossum can be traced to a single apical cell (Fig. 1 1 8), which is of large size, and, like that of the stem, approximately pyramidal in form. While the divi¬ sions show greater regularity than in the stem, still they are very much less so than in the higher Ferns. Segments are here cut off not only from the lateral faces of the apical cell, but also from its outer face. These outer segments help to form the root -cap, which, however, is not derived exclusively from these, but in part also from the outer cells of the lateral 236 MOSSES AND FERNS CHAP. segments. Each of the latter is first divided by a nearly vertical wall, perpendicular to its broad faces, into two “ sextant cells,” but beyond this no regularity could be discovered in the order of division in the segments, and the tissue at the growing point, especially in longitudinal section, presents a very confused arrangement of the cells. A little lower down two regions are discernible, a central cylinder (plerome), whose limits are not very clearly defined, and the periblem or cortex. A definite epidermis is not distinguishable. The first permanent tissue in the plerome cylinder, which is elliptical in section, arises in the form of small tracheids near the foci of the elliptical sec¬ tion. From here the formation proceeds to¬ wards the centre, and in the full-grown root the tracheary tissue forms a continuous band occupy¬ ing the larger axis of the section, the last- formed tracheids being the largest. On either side of this tracheary plate is a poorly de¬ fined mass of phloem, similar to that of the stem and leaf bundles. Here also no bundle- F,g. xx9.— Vascular bundle of the root of 0. pendulum, X 85. sheath is present, and the limits of the bundle are not clearly defined. In O. vulgatum the bundle of the root is diarch to begin with, but by the suppression of one of the phloem masses it becomes monarch. 1 he development of the sporangium has been studied by Goebel in O. vulgatum , and recently by Bower 2 in this species and in O. pendulum. The latter has been carefully examined by the writer, and the results confirm that of the latter investi- gatoi, except that it seems possible that the archesporium may Goebel (17), p. 390. 2 Bower (14). VIII THE PTER1D0P HYTA — OPHIOGLOSSA CEAC 237 be traced to a single cell, as Goebel asserts is probably the case in 0. vulgcitmn. A transverse section of the very young sporangiophore is somewhat triangular, the broader side corresponding to the outer surface of the sporangiophore. I he cells are very irre¬ gular in form, and no differentiation of the tissues is to be observed. Sections of somewhat older stages show in some cases, at least, a large epidermal cell occupying nearly the centre of the shorter sides of the triangular section. This cell has a larger nucleus than its neighbours, and is decidedly broader. A. B. The next stage was not observed, but a somewhat more advanced one shows a small group of inner cells (shaded in the figure), which appear to have arisen from the primary cell by a trans¬ verse wall, although this point is exceedingly difficult to deter¬ mine on account of the great similarity of all the cells (Fig. 120). This group of inner cells (or the single one from which they perhaps come) constitutes the archesporium, and by rapid division in all directions forms a large mass of cells whose contents become denser than those of the surrounding ones, between which and these, however, the limits are not very plain. Later, when the number of cells is complete, the difference 23S MOSSES AND FERNS CHAP. between them and the sterile tissue of the sporangiophore is much more evident. The cells lying outside of the archesporium divide rapidly both by longitudinal and transverse walls, and form the thick outer wall of the sporangium. In longitudinal sections, two rows of cells may be seen extending from the mass of arche- sporial cells to the periphery. In these rows the vertical walls have been more numerous than in the adjacent ones, so that the number of cells in these rows is greater. It is between these rows of cells that the cleft is formed by which the ripe sporangium opens. The cells of the ground-tissue adjoining the archesporium divide into several layers of narrow cells, which form the “ tapetum.” After the full number of cells is reached in the archesporium, their walls become partially disorganised, and the cells round VIII THE PTERIDOPHYTA — OPHIOGLOSSA CEPE 239 off and separate, exactly as in the sporogonium of a Bryophyte, and each cell is, potentially at least, a spore mother cell. Bower 1 states that only a part of the cells produce spores, and that the rest remain sterile and serve with the disorganised tapetal cells to nourish the growing spores. The final division of the spore mother cells into four spores is identical with that of the Bryophytes. At maturity the sporangium opens by a cleft, whose position is indicated as we have seen in the younger stages, and as the cells shrink with the drying of the ripe sporangiophore the spores are forced out through this cleft. Ophioglossum vulgatum and the other terrestrial forms show some points of difference when compared with 0. pendulum. These grow much more slowly, and longitudinal sections of the upper part of the subterranean stem show several leaves in different stages of development. Each leaf rudiment, as in O. pendulum , is covered by a conical sheath, formed at the base of the next older leaf, and these sheaths are open at the top, so that there is direct communication between the outside air and the youngest of these sheaths which encloses, as in the latter species, the youngest leaf rudiment and stem apex." In these terrestrial forms, also, the sporangiophore is longer stalked, and the lamina of the leaf more clearly separated from the petiole, which is not continued into it. The lamina is relatively broader and the venation more complex, in some species showing also free endings to the ultimate branches. The sporangia, too, project more strongly and are very evident (Fig. 1 1 3). Branch¬ ing of the roots occurs occasionally, and according to Rostowzew 3 may be either spurious or genuine. In the first place an adventive bud, which ordinarily would develop into a stem, develops a single root and then ceases to grow. This root appears to be formed directly from the main root, and as the latter continues to grow the effect is that of a true dichotomy. The latter does occur, but not frequently. The formation of adventitious buds upon the roots is the principal method of propagation of some species of Ophioglossum , whose prothallia, as we have seen, are apparently very seldom developed. Rostowzew states that these are not developed from the apical cell of the root, but arise from one of the younger segments, and the apical cell is produced from one of 1 Bower (14). 2 Rostowzew (1), p. 451- 3 Rostowzew, l.c. 240 MOSSES AND FERNS CHAP. VIII the outer cells of the young segment, but is covered by the root-cap, through which the bud afterwards breaks. The sheath covering the first leaf of the bud is formed from the cortex of the root and the root-cap. Differing most widely from the other species in general appearance is the curious epiphytic O. ( Cheiroglossa ) palmatum. In this the leaf is dichotomously branched, and instead of a single sporangiophore there are a number arranged in two rows along the sides of the upper part of the petiole and the base of the lamina. The genus Botrychium includes several exceedingly variable species, the simplest forms, like B. simplex (Fig. I 22, A, B), being very close to Ophioglossum, while leading from these is a series ending in much more complicated types, of which B. Virginianum is a good example. In B. simplex the lamina of the leaf is either entirely undivided, as in most species of Ophioglossum, or once pinnatifid. From this there is a complete series to the ample decompound leaf of B. Virginianum. When the other parts of the plant are studied we find that this greater com¬ plexity extends to these as well. Thus the sporangiophore is also decompound, and the sporangia entirely free, and showing an approach to that found in such Ferns as Osmunda , and the dichotomous venation of the simpler forms approaches the pinnate type in B. Virginianum. The tissues, especially the vascular bundles, are also more highly differentiated in these species. Under favourable conditions well-grown plants of B. Vir¬ ginianum reach a height of 50 cm. or more, and the sterile lamina of the leaf, which is triangular in outline, may be 30 to 40 cm. in breadth, and from three to four times pinnate. The texture of the leaf is membranaceous and not fleshy like that of Ophioglossum and most species of Botrychium. The sporangiophore is twice or thrice pinnate. The plant sends up a single leaf each year from the underground stem, which is upright and several centimetres in length in old specimens. The roots are thick and fleshy, and much smaller at the point of insertion. As in Ophioglossum each root corresponds prob¬ ably to a leaf, but the roots branch frequently, so that the root system is much better developed than in Ophioglossum. The secondary roots of B. Virginianum arise laterally, and in much the same way as those of the higher Ferns. As in the terres- Fig. 122.— A, B, Botrychium simplex (Hitch), natural size; C, B. ternaium (Sw.), Xj; D, leaf segment of B. lunaria (Sw.) ; E, leaf segment of B. Virginianum (Sw.), natural size ; F, portion of sterile leaf segment of Helminthostachys Zeylanica (Hk.) ; G, fragment of the sporangiophore of the same enlarged. A, B, C after Luerssen ; D, F after Hooker. R 242 MOSSES AND FERNS CHAP. trial species of Ophioglossum , the development of the leaves is very slow. In most species of Botrychium the relation of the leaf base to the young bud and stem apex is the same as in Ophioglossum , except that the sheath is more obviously formed from the leaf base ; but in B. Virginianum the sheath is open on one side, and more resembles a pair of stipules. Fig. 123, A shows the stem and terminal bud of a plant of this species with all but A Fig. 123. — Botrychium Virginianum (Sw.). A, Rhizome and terminal bud of a strong plant, the roots and all but the base of the oldest leaf removed, X 1 ; B, longitudinal section of the bud, X3 ; st , the stem apex ; I. II. III., the leaves ; C, transverse section of the petiole, X4 ; D, transverse section of the rhizome, X about 16 ; P, the pith ; ;//, medullary rays ; jr, xylem ; c, cambium ; / */t , phloem ; sh, endodermis. the base of the leaf of the present year cut away, and B the same with the bud cut open longitudinally. At this stage the parts of the leaf for the next year are well advanced, and the formation of the individual sporangia just begun. The leaf for the second year already shows the sporangiophore clearly evident, and the leaf which is to unfold in three years is evident, but the sporangiophore not yet differentiated. At the base of the youngest leaf is the stem apex. The whole bud is covered in this species with numerous short hairs, which are VIII THE P TERIDOPHYTA — OPHIOGLOSSA CEPE 243 also found in B. ternatum and some other species, but in B. simplex and the other simpler species it is perfectly smooth, as in Ophioglossum. The young leaves in B. Virginianum are bent over, and the segments of the leaf are bent inward in a way that recalls the vernation of the true Ferns. The spor- angiophore grows out from the inner surface of the lamina, and its branches are directed in the opposite direction from those of the sterile part of the leaf. The vascular bundles of the stem are much more prominent than in Ophioglossum , and form a hollow cylinder, with small gaps only corresponding to the leaves. This cylinder shows the tissues arranged in a manner that more nearly resembles the structure of the stem in Gymnosperms or normal Dicotyledons than anything else. Surrounding the central pith (Fig. 123, P) is a ring of woody tissue (x) with radiating medullary rays (in'), and outside of this a ring of phloem, separated from the xylem by a zone of cambium (c), so that here alone among the Ferns the bundles are capable of secondary thickening. The whole cylinder is enclosed by a bundle-sheath (endodermis) consisting of a single layer of cells. The cortical part of the stem is mainly composed of starch-bearing parenchyma, but the outermost layers show a formation of cork, which also is formed in the cortical portions of the roots. The free surface of the stem apex is very narrow, and the cells about it correspondingly compressed. The apical cell f Fig. 124, A, B), seen in longitudinal section, is very deep and narrow, but as comparison of cross and longitudinal sections shows, has the characteristic pyramidal form, and here there is no doubt that only lateral segments are cut off from it. Holle’s 1 figure of Botrychium rutcefolium closely resembles B. Virginianum, and probably the other species will show the same form of apical cell. The divisions are decidedly more regular in the segments of B. Virginianum than in Ophio¬ glossum, and can be more easily followed, although here, too, as the division evidently proceeds very slowly, it is difficult to trace the limits of the segments beyond the first complete set, which in transverse section are sufficiently clear. The first division divides the segment into an inner and an outer cell, Holle (1), Pl. IV. Fig. 32. 1 244 MOSSES AND FERNS CHAP. the former probably being directly the initial for the plerome cylinder. The outer cell by later divisions forms the cortex, and the epidermis which covers the very small exposed surface of the stem apex. Here, as in Opkioglossum , it is impossible to determine exactly the method of origin of the young leaves, one of which probably corresponds to each segment of the apical cell, but as soon as the leaf can be recognised as such it is already a multicellular organ. It grows at first by an apical cell which seems to correspond closely in its growth with that of the stem. From almost the very first (Fig. 124) Fig. 124 .-Botrychium Virginianum (Sw.). A, Longitudinal section of the stem apex of a young plant, X 260 ; B, cross-section of a similar specimen ; L, the youngest leaf. the growth of the leaf is stronger on the outer side, and in consequence it bends inward over the stem apex. The arrangement of the tissues of the fully -developed stem shows, as we have seen, a striking similarity to those in the stems of many Spermaphytes. The xylem of the strictly collateral bundle is made up principally of lar-e prismatic tracheids (Fig. 125), whose walls are marked with bordered pits not unlike those so characteristic of the Coni- ferae, but somewhat intermediate between these and the elongated ones found in most Ferns. The walls between the pits are very much thickened, and the bottoms of VIII THE P TEPID OPH } "TA—OPHIOGLOSSA CEJE 245 corresponding pits in the walls of adjacent tracheids are separated by a very delicate membrane. At intervals medullary rays, one cell thick, extend from the pith to the outer limit of the xylem. The cells are elongated radially, and have uniformly thickened walls and granular contents. The phloem consists of large sieve-tubes and similar but smaller parenchymatous cells. No bast fibres or sclerenchy- matous cells are present. The whole cylinder is bounded by a single layer of cells somewhat compressed radially, forming Fig. 125.-A, Part of a cross-section of the stem bundle of B. Virginianum, X soo.-lettering as in Fig. 123 ; B, a portion of the tracheary tissue, showing the peculiarly pitted walls, X400. the endodermis or bundle -sheath. Between the xylem and phloem is a well-defined layer of cambium by whose growth the thickness of the vascular cylinder is slowly but constantly added to, and as a result there is a secondary growth of the stem strictly comparable to that of the Dicotyledons. The outer layer of the cortex (the epidermis is quite absent) develops cork, but not from a definite cork cambium.1 These cork cells arise by repeated tangential divisions in cells 1 Holle (1), p. 249. 246 MOSSES AND FERNS CHAP. near the periphery, and have in consequence the same regular arrangement seen in similar cells of the higher plants. A cross-section of the petiole of the earliest leaves of the young plant show but a single nearly central vascular bundle, but as the plant grows older the number becomes much larger, and may reach ten.1 In leaves of moderate size there are usually about four, and these are arranged symmetrically. The ground tissue is composed mainly of large thin-walled parenchyma and a well-marked epidermis. The fibrovascuiar Fig. 126.— Part of a vascular bundle from the petiole of B. Virginianum, X245; _ry, xylem ; fih, phloem ; s,s, sieve-tubes ; B, two sieve-tubes in longitudinal section, X 4Q0 ; sp, sieve-plates ; n, nuclei. bundles are arranged in two groups, right and left, and where there are four of them the inner ones are the larger, and in cross-section crescent -shaped. The xylem here occupies the middle of the section, and is completely surrounded by the phloem, i.e. the bundle is concentric, like that of the true Ferns. In B. lunana the bundle has the phloem only perfectly developed on its outer side and approaches the collateral form. B. ternatum and B. lunana , while having concentric bundles, Luerssen (8), p. 588. 1 VIII THE PTERIDOPH YTA—OPHIOGLOSSA CEAC 247 also have the phloem more strongly developed on the outer side. The tracheary tissue is much like that of the stem, but the tracheids are smaller and the walls thinner. The phloem is composed also of the same elements, large sieve-tubes, arranged in a pretty definite zone next the xylem, and smaller cells of similar appearance, but not showing the multinucleate character or perforated transverse walls of the latter. The sieve-tubes are large (Fig. 126), and in longitudinal section are seen to consist of rows of wide cells with either hori¬ zontal or oblique division walls. The transverse walls separating two members of a sieve-tube are somewhat swollen and show small perforations, which are not always easily demonstrated. According to Janczewski 1 these pits do not penetrate the membrane between the cells, but Russow’s 2 assumption that there is direct communication between the cells is correct, although difficult to prove. Russow also states that callus is present in the sieve -plates of Botrycluum , although poorly developed. According to Janczewski3 the pores are not confined to the transverse walls, but may also occur, but much less frequently, in the longitudinal walls. The contents of the sieve-tubes consist of a thin parietal layer of protoplasm in which numerous nuclei are imbedded. Little glistening globules are also found, especially close to the openings of the pores of the sieve-plates. The lamina of the sterile segment of the leaf is composed of a spongy green mesophyll, more compact on the upper surface. The epidermal cells show the wavy outlines char¬ acteristic of the broad leaves of other Ferns, and develop stomata only upon the lower side of the leaf. The Root The roots arise singly at the bases of the leaves, and in older plants branch monopodially. Like those of Ophioglossuin they have no root-hairs, but the smooth surface of the younger roots becomes often strongly wrinkled in the older ones. Sections either transverse or longitudinal, through the root tip, when compared with those of Ophioglossuin, show a very much greater regularity in the disposition of the cells. This is less marked in B. tevncitilfn, and probably an examination 1 Janczewski (4). 2 Russow (5). 3 Janczewski (4), p. 69. 248 MOSSES AND FERNS CHAP. of such forms as B. simplex will show an approximation to the condition found in Ophioglossu m , although Holle’s 1 figure of B. lunaria shows even greater regularity in the arrangement of the apical meristem than is found in B. Virginianum. A careful examination of this point is much to be desired. The first wall in the young lateral segment is the sextant wall, as in the higher Ferns, and divides the segment into two cells of unequal depth. The next wall divides the larger of these cells into an inner and an outer one, the former becoming the initial of the central plerome cylinder, the outer one, together with the whole of the smaller semi-segment, giving rise to the Fig. 127. Botrychium Virginianum (Sw.). A, Longitudinal ; B, transverse sections of the root apex. X 200 ; pi, plerome. cortex, in which the divisions are very similar to, but some¬ what less regular than in Equisetum and the leptosporangiate Ferns. As usual in roots of this type segments are also cut off from the outer face of the apical cell, but I have never seen, either in B. Virginianum or B. ternatum , any indication that the growth of the root - cap was due exclusively to the development of these segments, as Ftolle states both for B. lunaria and Ophioglossum vulgatum. In both species of Botrychium examined by me the growth of the root-cap was evidently due in part to the division of cells in the outer part of the lateral segments, so that in exactly median sections 1 Holle (1). VIII THE PTERIDOPHYTA — OPHIOGLOSSA CE.E 249 there was not the clear separation of the root -cap from the body of the root that is so distinct in Equisetum, for example. The central fibrovascular cylinder of the root is not provided with a definite endodermis, and its limits are not clearly defined. It varies in the number of xylem and phloem masses, even in the same species. In B. Virgimanum the larger roots show three or four xylem masses (Fig. 128). B. ternatum has a usually triarch bundle, while B. lunana is commonly diarch.1 The elements both of the xylem and Fig. 128.— Tetrarch vascular bundle of the root of B. Virginianum, X85. phloem are much like those in the stem and do not need any special description. The roots increase considerably in diameter as they grow older, but this enlargement does not take place at the base, where the root is noticeably constricted. The enlargement is due entirely to the cortical tissue, and is mainly simply an enlargement of the cells. The diameter of the central cylinder remains the same after it is once formed. In the outer part of the root, as in the stem, there is a develop¬ ment of cork. 1 Holle (1), p. 245. 250 MOSSES AND FERNS CHAP. The Sporangium In the simplest forms of B. simplex the sporangia, which are much larger than those of B. Virgmianum , form two rows very much as in Ophioglossum ; but in all the more complicated forms the sporangiophore branches in much the same way as the sterile part of the leaf, and the ultimate segments become the sporangia. In B. Virginianum the development of the individual sporangia begins just about a year previous to their ripening, and if the plants are taken up about the time the spores are shed, the earliest stages may be found. The sporangiophore is at this time thrice pinnate in the larger specimens, and an examination of its ultimate divisions will show the youngest recognisable sporangia. These form slight elevations growing smaller toward the end of the segment (Fig. 129), and exact median sections show that at the apex of the broadly conical prominence which is the first stage of the young sporangium there is a large pyramidal cell with a truncate apex. Holtzman 1 thinks the sporangium may be traceable to a single cell, and that the divisions at first are like those in a three-sided apical cell. I was unable to satisfy myself on this point, but the youngest stages found by me in which the sporangial nature of the outgrowths was unmistakable, would not forbid such an interpretation, although there was no doubt that the basal part of the sporangium is derived in part from the surrounding tissue. From the central cell, by a periclinal wall, an inner cell, the archesporium, is separated from an outer one. The outer cell divides next by cross walls, and this is followed by similar divisions in the inner cells (Fig. 129). The succeeding divi¬ sions in the outer cells are now mainly periclinal, and transform the four cells lying immediately above the archesporium into as many rows of tabular cells. Growth is active in the meantime in the basal part of the sporangium, which projects more and more until it becomes almost spherical. To judge from the somewhat incomplete account given by Goebel 2 of B. lunana , this species corresponds closely in its early stages to that of B. Vtrgimanum. The later divisions in the arche¬ sporium do not apparently follow any definite rule, but divi- 2 Goebel (3). 1 Holtzman (1). VIII THE P TERIDOPH 1 'TA—OPHIOGL OSSA CE.E 251 sions take place in all directions until a very large number of cells is formed. The cells immediately adjoining the sporogenous tissue divide into tabular tapetal cells, as in Ophioglossum. The sporangium shortly before the isolation of the spore mother cells (Fig. 129, C) is a nearly globular body with a thick, very short stalk. The central part of the upper portion is occupied by the sporogenous tissue sur¬ rounded by a massive wall of several layers of cells, of which the inner ones constitute the tapetum. d he central cells, as Fig. 129 .—Botrychium Virginianum (Sw.). Development of the sporangia. A, I, 2, Very young sporangia; B, a somewhat older one, X480 ; C, older sporangium, X240, all median longitudinal sections, the sporogenous cells have the nuclei shown. usual, have larger nuclei, and more granular contents than the outer ones. The stages between this and the ripe sporangium were not seen, so that it cannot be stated positively whether all the cells of the sporogenous tissue (which seems probable) or only a part of them, as in Ophioglossum , develop spores. The stalk is traversed by a short vascular bundle, which is first evident about the time that the number of sporogenous cells is complete, and joins directly with the young vascular bundle of the leaf segment (Fig. 1 29, C). The ripe sporangium opens by a transverse slit, as in Ophioglossum. 252 MOSSES AND FERNS CHAP. The presence of fungous filaments in the roots of the Ophioglossaceae has been repeatedly observed, and has been the subject of recent investigations by Atkinson,1 who is inclined to regard them as of the same nature as the mycorrhiza found in connection with the roots of many Dicotyledons, especially Cupuliferse. Atkinson asserts that he finds them invariably present in all the forms he has examined ; but Holle 2 states that, while they are usually present in Ophioglossum , he has found strong roots entirely free from them, and that in Botrychium rutcefolium they were mainly confined to the diarch roots, and that this is connected with a weakening of the growth of the root through the growth of the fungus, by which the triarch bundle of the normal fully-developed root is replaced by the diarch form of the weaker one. The third genus of the Ophioglossaceae, Helminthostachys , with the single species H. Zeylanica, is in some respects inter¬ mediate between the other two, but differs from both in some particulars. The sporophyte, which alone is known, and that very imperfectly, has a creeping fleshy subterranean rhizome, with the insertion of the leaves corresponding to Ophioglossum pendulum. According to Prantl,3 who has made a somewhat careful study of a plant, the roots do not show any definite relation to the leaves, as Holle claims is the case in the other genera. The plant sends up a single leaf, which may reach a height of 30 to 40 cm. or more, and as in the Ophioglossum vulgatum and B. Virginianum , the sporangiophore arises from the base of the sterile division of the leaf. The latter is palmately lobed, and the primary divisions are also divided again. Often the primary divisions are ternately arranged, as in the larger species of Botrychium. The venation is different from that of the other Ophioglossacem, and is extremely like that of Angioptens. Each pinnule is traversed by a strong midrib, from which lateral dichotomously branched veins run to the margin. In regard to the structure of the sheath that encloses the young leaf and stem apex, Helminthostachys resembles Ophioglossu m . Prantl 4 states that the vascular cylinder of the stem is solid on the lower surface, but on the upper side has the openings corresponding to the leaf insertions. Two primary bundles are formed for each leaf, which fork before they enter the petiole, 1 Atkinson (2). 2 Holle (1). 2 Prantl (7). 4 Prantl, l.c. VIII THE P TEPID OPH VTA — OPHIOGL OSSA CE.-E 253 so that there are four bundles at the base of the petiole. Higher up a cross-section shows ten bundles arranged about the periphery, and an inner one, formed by the branching of one of the others upon the upper side. This inner bundle, and those of the upper side of the stalk, furnish the bundles for the sporangiophore. The sporangiophore is long-stalked and in general appear¬ ance intermediate between that of the other genera, but a careful examination shows that it is much more like that of Botrychium. It is pinnately branched, but in an irregular way, and the small branchlets bear crowded oval sporangia, which open longitudinally on the outer side, and not transversely as in the other genera. The tips of the branches, instead of forming sporangia as in Botrychium, develop into green leaf¬ like lobes, which upon the shorter branchlets are often arranged in a rosette of three or four together, with the sporangia close below them (Fig. 122, D ). This at first sight looks as if the sporangia were produced upon the lower side of these, like Equisetum , but a very slight examination shows at once that this is only apparent, and the sporangia are undoubtedly outgrowths of the branches as in Botrychium. The green lobes are seen to be only the vegetative tips of the branches, or perhaps better comparable to such sterile leaf segments as are not uncommon in Osmunda Claytoniana. Unfortunately the life history is absolutely unknown, and its histology is also too imperfectly known to make it possible at present to determine its exact relation on the one hand to the other Ophioglossaceae, and on the other to the Marattiaceae and Filices. CHAPTER IX MARATTI ACE/E - ISOETACE^E The Marattiacece The Marattiacese at the present time include four genera with about twenty-five species, confined exclusively to tropical regions. In a fossil condition they are much more numerous and diversified, and according to Solms-Laubach 1 comprise the majority of the carboniferous and pre-carboniferous Ferns. Recently a good deal of attention has been paid to these Ferns, and our knowledge of their life-history and structure is fairly complete. Some of them are Ferns of gigantic size. Thus the stem of Angiopteris evecta is sometimes nearly a metre in height and almost as thick, with leaves 5 to 6 metres in length, and some species of Marattia are almost as large. The other genera, Kaulfussia and Dancea , include only species of small or medium size. While in the structure of the tissues and the character of the sporangia these show resemblances to the Ophioglossaceae, their general appearance is more like that of the true Ferns, with which they also agree in the circinate vernation of their leaves. The sporangia are borne upon the lower surface of ordinary leaves, as in most leptosporangiate Ferns, but the sporangia themselves are very different, and are more or less completely united into groups or synangia, which open either by longitudinal slits or, in Dancea , by a terminal pore. The base of the leaf is provided with a pair of fleshy stipules, which possibly correspond to the sheath at the base of the petiole in Botrychium. 1 Solms-Laubach (2), p. 142. CHAP. IX MA RA TTIA CEAE—ISOE TA CEAE 255 The Gametophyte The germination of the spores and development of the prothallium were first investigated by Luerssen 1 and Jonkman 2 in Angiopteris and Marattia , and later by the latter investigator for Kaulfussia? The spores are of two kinds, bilateral and tetrahedral, but the former are more common. They contain no chlorophyll, but oil is present in drops of varying size, as well as other granular bodies. The nucleus occupies the centre of the spore and is connected with the wall by fine protoplasmic filaments. The wall of the spore is colourless and shows three coats, of which the outer one (perinium) is covered with fine tubercles. Germination begins within a few days and is first indicated by the development of chlorophyll. This does not, as Jonk¬ man 4 asserts, first appear in amorphous masses, but very small, faintly-tinted chromatophores appear between the large oil- drops, and these rapidly increase in size and depth of colour as germination proceeds, and their number increases by the ordinary division. In the bilateral spores the exospore is burst open above the thickened ventral ridge found in these spores, and the growing endospore slowly protrudes through this. The spore enlarges to several times its original diameter before the first division occurs, and forms a globular cell in which the large chloroplasts are arranged peripherally. The first division takes place about a month after the spores are sown, and is perpendicular to the longer axis of the cell, dividing it either into two equal parts, or the lower may be much smaller and develop into a root-hair. In the former case each cell next divides by walls at right angles to the first, and the resulting cells are arranged like the quadrants of a circle, and one of these cells becomes the two-sided apical cell from which the young prothallium for a long time grows (Fig. 130), much as in Aneura. This type of prothallium, according to Jonkman,5 is commoner in Marattia than in Angiopteris, where more commonly a cell mass is the first result of germination. This latter is usually derived from the form where a root-hair is developed at first. In this case only the larger of the primary 1 Luerssen (5). 2 Jonkman (1). 3 Jonkman (2). 4 Jonkman, Bot. Zeit. 1S7S, p. 136. 5 Jonkman, l.c. p. 146. 256 MOSSES AND FERNS CHAP. cells give rise to the prothallium. In the larger cell divisions take place in three directions and transform it into a nearly globular cell mass, terminated by four quadrant cells, one of which usually becomes the apical cell, much as in the flat pro¬ thallium. In exceptional cases the first divisions are in one plane and a short filament results. As soon as the apical cell is established it grows in pre¬ cisely the same way as the similar cell in the thallus of a A. Fig. 130. — Angiopteris evectaiYlottm). Germination of the spores, — A, B, X220 ; C, X 175 ; sp, spore membrane ; x} apical cell (after Jonkman). Liverwort, and produces a thallus of much the same form and structure. As the prothallium grows older, however, a cross¬ wall forms in the apical cell, and this is followed by a longi¬ tudinal wall in the outer one, forming two similar cells which, by further longitudinal divisions, may produce a row of marginal initials, and the subsequent growth of the prothallium is due to the divisions and growth of this group of initial cells (Fig. I3L A). At first the prothallium has a spatulate form, but before the IX MA RA TTIA CE^E—ISOE TA CERE 257 single apical cell is replaced by the group of marginal initials, the outer cells of the segments grow more rapidly than the inner ones, and the segments project beyond the apical cell, which comes to lie in a depression between the two lobes formed by the outer parts of the segments, and the prothallium assumes the heart -shape found in most homosporous Ferns. The secondary initial cells vary in number with the width of the indentation in which they lie. Seen from the surface they are oblong in shape, but in vertical section are nearly semicircular (Fig. 1 3 1, B). Basal segments are cut off by a wall that extends the whole depth of the prothallium, and the seg¬ ment is then divided by a horizontal wall into a dorsal and ventral cell of nearly equal size. The divisions are more numerous in the ventral than in the dorsal cells of the segment, this difference first being manifest some distance back of the apex. Owing to this, a strongly projecting, nearly hemispherical cushion¬ like mass of tissue is formed upon the ventral surface. The superficial cells of both sides of the prothallium have a well-marked cuticle. Numer¬ ous brown root-hairs, which, like those of the simpler Liverworts, are unicellular and thin - walled, grow out from the cells of the lower surface, especially from the broad midrib. The full-grown prothallium in M. Douglasii is some¬ times a centimetre or more in length (Fig. 132), and tapers from the broad heart-shaped forward end to a narrow base. In Angiopterisx it is more nearly orbicular. In both genera it is dark-green in colour, looking very much like the thallus of Anthoceros lezvis, and like this too is thick and fleshy in texture. A broad midrib extends for nearly the whole length 1 Farmer (3). S Fig. 131. — Mnrcittia Douglasii (Baker). A, Hori¬ zontal section of prothallium apex, with two initials, X 160. B, Longitudinal section of a similar growing point ; d, dorsal ; z/, ventral segment. 258 MOSSES AND FERNS CHAP. of the thallus and merges gradually into the wings, which are also several-layered, nearly or quite to the margin. The very old prothallia sometimes branch dichotomously (Fig. 132, B, C), and the process is identical with that in the thallose Hepaticse. The two growing points are separated by a median lobe in the same way, and the midrib with the sexual B. C. organs upon it forks with it, exactly as we find, for example the antheridial receptacle forking in Fimbriaria Californica (Fig! i’ A)- _ Besides this form of branching, which is not common, adventitious buds are produced upon the margin of the thallus very fiequently. These grow in precisely the same way as the mam prothallium, and after a time may become detached and form independent plants ; or they may develop sexual organs (mainly antheridia) while still connected with the mother IX MA RA TTIA CEA1- ISO E TA CEAI 259 plant. The duration of the prothallium is apparently unlimited, so long as it remains unfecundated. The writer kept prothallia of Marattia Douglasii for nearly two years, during which they grew continuously and finally reached a length of over two centimetres. At the end of this time they were growing vigorously, and there was nothing to indicate the slightest decrease in their vitality. The prothallia are monoecious, although not infrequently the smaller ones bear only antheridia. The latter always appear first, and are mainly found upon the lower side of the midrib, but may also occur upon the upper side. The arche- gonia are confined to the lower surface of the midrib, and as they turn dark brown if they are not fertilised, they are visible to the naked eye as dark brown specks studding the broad thick midrib. Both antheridia and archegonia resemble closely those of the Ophioglossaceae. The antheridium arises from a single superficial cell which first divides into an inner cell, from which the sperm cells are derived, and an outer cover cell (Fig. 133, A). The latter divides by several curved vertical walls (Figs. E-G) which intersect, and the last wall cuts off a small triangular cell (0), which is thrown off when the antheridium opens, and leaves an opening through which the sperm cells are ejected. The inner cell, by repeated bipartitions, gives rise to a large number of polyhedral sperm cells. Before the full number of these is complete, cells are cut off from the adjacent prothallial cells, which completely enclose the mass of sperm cells. As in other Archegoniates, the nucleus of the sperm cell, after its final division, shows no nucleolus. The first sign of the formation of the spermatozoid that could be detected was an indentation upon one side, followed by a rapid flattening and growth of the whole nucleus. The cytoplasmic prominence which, according to Strasburger,1 is the first indication of the formation of the spermatozoid, could not be certainly detected. The main part of the sperma¬ tozoid stains strongly with alum-cochineal, and is sharply differen¬ tiated against the colourless cytoplasm, and for some time shows the characteristic nuclear structure. The origin of the cilia was not very clearly made out, but probably, as Strasburger claims, they are direct outgrowths of the forward end. The free spermatozoid (Fig. 133, I) is a flattened band, somewhat blunt 1 Strasburger (1 1), vol. iv. p. 116. 26o MOSSES AND FERNS CHAP. behind and tapering to a fine point in front ; attached to a point just -back of the apex are several fine cilia. The body shows only about two complete coils. The youngest archegonia are met with some distance back of the growing point, and apparently any superficial cell is poten¬ tially an archegonium mother cell. The latter divides usually into three superimposed cells (Fig. 134, A), of which the lowest (b) forms the base of the archegonium. From the central one by a transverse division are formed the primary neck canal cell and the central cell. Each of these divides again transversely. In the upper one this division is often incomplete and confined to the nucleus ; but in the central cell the division results in the separation of the ventral canal cell from the ovum. Before the separation of the primary neck canal cell from the central cell, the cover cell divides as in the Liverworts into four cells bv intersecting vertical walls, and each of these cells by further IX MARA TT1A CEAE—ISOE TA CEsE 261 obliquely transverse walls forms a row of about three cells, and these four rows compose the short neck. The canal cells are very broad and the egg cell small, so that after the archegonium opens it occupies but a small part of the cavity left by the disintegration and expulsion of the canal cells. Before the archegonium is mature, flat cells are cut off from the adjacent prothallial tissue as in the antheridium (Fig. 134, D). The neck of the ripe archegonium projects but little above the surface of the prothallium, and in this respect recalls both the Fig. 134. _ Marattia Douglasii (Baker). A-D, Development of the archegonium, X 450 ; E, section of the fertilised egg, showing the spermatozoid ( sp ) in contact with its nucleus, X485 ; F, successive longitudinal sections of a young embryo, X 225 ; b, b, the basal wall, the arrow points towards the archegonium. lower Ophioglossacese and the Anthocerotese. The ripe ovum is somewhat elliptical, and slightly flattened vertically. Its upper third is colourless and nearly hyaline. This is the “ receptive spot,” and it is here that the spermatozoid enters. The nucleus is of moderate size, and not rich in chromatin ; a small but distinct nucleolus is present. The spermatozoid retains its original form after it first enters the egg, and until it comes in contact with the membrane of the egg nucleus. It afterwards contracts and assumes much the appearance of the 262 MOSSES AND FERNS CHAP. nucleus of the sperm cell previous to the differentiation of the spermatozoid. The two nuclei then gradually fuse, but all the different stages could not be traced. Before the first division takes place, however, but one nucleus can be seen, and this much resembles the nucleus of the unfertilised egg. After fertilisation the egg enlarges to several times its original size before dividing. The first (basal) wall is transverse and is followed in each half by two others, the median and octant walls. The nearly globular embryo is thus divided into F‘g- 135- Marattia Douglasii (Baker). Embryogeny. A, Longitudinal ; B, transverse sections of embryos, X215 ; C, vertical section of an older embryo, showing its position in the prothallium, X72 ; st, the stem ; pr, prothallium ; D, upper part of the same embryo, X215. eight similar cells, each having the tetrahedral form of a globe octant. The next divisions are not perfectly understood, and evidently are not absolutely uniform in all cases. All the octants at first show nearly uniform growth, and the embryo retains its nearly oval form (Figs. 134, F, 135, A). The first division in the octants is essentially the same, and consists in a series of anticlinal walls, before any periclinal walls appear, so that we may say that for a short time each octant has a dis¬ tinct apical growth, and there are eight growing points. The IX MA RA TTIA CEsE—ISOE TA CERE 263 older embryo shows an external differentiation into the first leaf, stem, and root, but the foot is not clearly limited at first. The basal wall separates the embryo into two regions, epibasal and hypobasal. From the former the cotyledon and stem apex are derived, from the latter the root and foot. The cotyledon arises from the anterior pair of epibasal octants, which are in the Marattiacese, unlike all the other Ferns, turned away from the archegonium opening. In the earliest stages where the cotyledon is recognisable, no single apical cell could be made out, and later the growth is very largely basal. At first the growth is nearly vertical, but it soon becomes Fig. 136. — Marattia Douglasii{ Baker). A, Cross-section of the young sporophyte at the junction of the cotyledon and stem ; st, the apical meristem of the stem, X215 ; B, the stem apex of the same, X 430 ; C, longitudinal section of the stem apex of a plant of about the same age, X 215 ; tr, the primary tracheary tissue ; r2, the second root. stronger upon the outer side, and the leaf rudiment bends inwards. At this stage the different tissues begin to be dis¬ tinguishable. Somewhat later the tip of the cotyledon becomes flattened, and still later there is a dichotomy of this flattened part which thus forms a fan-shaped lamina (Fig. 138). The first tissue to be recognised is the vascular bundle, which traverses the centre of the petiole and at first consists of uniform thin-walled elongated cells (procambium). This forma¬ tion of procambium begins in the centre of the embryo and proceeds in three directions, one of the strands going into the cotyledon, one in an almost opposite direction to the primary 264 MOSSES AND FERNS CHAP. root, and a very much shorter one to the young stem apex, which lies close to the base of the cotyledon. The outer layer of cells of the cotyledon forms a pretty clearly defined epidermis separated from the axial procambium strand by several layers of young ground-tissue cells. The apex of the young stem is occupied in some cases, at least by a single apical cell, which probably is to be traced back directly to one of the original octants of the embryo. Whether is is a ways the case in the youngest stages cannot be de¬ termined until further investigations are made. Farmer 1 was 1 Farmer (3), p. 267. IX MARA TTIA CEjE—ISOE TA CE.E 265 unable to make out a single initial in Angiopteris , which other¬ wise agrees closelv with Marattia. The study of the root was confined mainly to the older embryos, and although some variation is noticed, it is pretty certain that there is a single apical cell, not unlike that found in the Ophioglossacem. Whether this can be traced back to one of the primary hypobasal octants, it is impossible now to say; but Farmer’s1 statement that in Angiopteris there is at first a three-sided apical cell would point to this. Unfortunately my own preparations of Marattia were too incomplete to decide this point in the latter. In the older root the form of the apical cell was usually a four-sided prism, from all of whose faces segments were cut off, although sometimes an approach to the triangular form found in the Ophioglossacese was observed. The foot is much less prominent than in Botryclimm , and in this respect the Marattiacese are more like Ophioglossuni ? In Marattia all the superficial cells of the central region of the embryo become enlarged and act as absorbent cells for the nourishment of the growing embryo. As the embryo grows, the surrounding prothallial tissue divides rapidly, and a massive calyptra is formed which com¬ pletely encloses the young sporophyte for a long time. Owing to the position of the cotyledon and stem, which grow up vertically through the prothallium, a conspicuous elevation is formed upon its upper side, through which the cotyledon finally breaks. A similar elevation is formed by the calyptra upon the lower side, through which the root finally penetrates, but not until after the cotyledon has nearly reached its full development. The prothallium does not die immediately after the young sporophyte becomes independent, but may remain alive for several months afterwards, much as in Botrychium. The first tracheary tissue arises at the junction of the bundles of the cotyledon, stem, and root. These primary tracheids are sPofl; and their walls are marked with reticulate thickenings. From this point the development of the tracheary tissue, as well as the other elements of the bundles, proceeds toward the apices of the young organs. The formation of the secondary tracheids is always centripetal. Short hairs with cells rich in tannin, and staining strongly 1 Farmer (3), p. 268. 2 Mettenius (2), PI. XXX. 266 CHAP. MOSSES AND FERNS with Bismarck-brown, occur sparingly upon the leaves and stem of the young sporophyte. The fully-developed cotyledon has the fan-shaped lamina somewhat lobed, and the two primary veins arising from the forking of the original vascular bundle usually fork once more, so that the venation is strictly dichotomous in character. Farmer 1 figures the cotyledon of Angiopteris as more spatulate in form, with a distinct midrib, but this is never the case in M. Douglasii. The nearly cylindrical petiole is deeply channeled upon the inner side, and the single axial vascuiar bundle is almost circular in section. While the crescent-shaped mass of tracheary tissue is completely surrounded by the phloem, the latter is much more strongly developed upon the outer side, and the bundle approaches the collateral form of Ophioglossum. In¬ deed, if the tannin cells, which are found here, belong to the cortex, as Farmer asserts to be the case in Angiopteris, the Fig. 138. — Horizontal section of the lamina of the cotyledon of . . M. Douglasii, X260. bundle would be truly collateral, as these are immediately in contact with the tracheids. The lamina of the cotyledon is similar in structure to that of the later leaves, and differs mainly in the smaller development of the mesophyll. The smaller veins have the xylem reduced to a few (1-3) rows of tracheids upon the upper side of the collateral bundle. Stomata of the ordinary form occur upon the lower side of the leaf. As the root finally breaks through the calyptra and pene¬ trates into the earth, numerous fine unicellular root -hairs develop from the older parts, but the tip for some distance remains free from them. Owing to the numerous irregularities in the cell divisions, the exact relation of the tissues of the older parts of the root to the segments of the apical cell is 1 Farmer (3), Figs. 19-21. IX MA RA TTIA CE.E—ISOE TA CEAi 267 --F. impossible to determine, and evidently is not always exactly the same. The root -cap is derived mainly from the outer segments of the apical cell, but also to some extent from the outer cells of the lateral segments ; and the plerome cylinder, where the base of the apical cell is truncate, is formed mainly from the basal segments, but in part as well from the inner cells of the lateral segments. The vascular cylinder of the root is usually tetrarch. At four points near the periphery small spiral or annular tracheids appear, and from them the formation of the larger secondary tracheids pro¬ ceeds toward the centre. The phloem is made up of nearly uniform cells with moderately thick colourlesswalls. A bundle- sheath is not clearly to be made out (Fig. 137)- The cotyledon is des¬ titute of the stipules found in the perfect leaves of the Marattiaceae, but they are well developed in the third leaf, where they form two conspicuous appendages clasping the base of the next youngest leaf. The edges of these stipules are somewhat serrate, and the edges of the two meet, much like two bivalve shells. The strictly dichotomous character of the cotyledon is gradually replaced in the later leaves by the pinnate arrangement, both of the divisions of the leaf and the venation. This is brought about in both cases by an unequal dichotomy, by which one branch develops more Fig. 139. — Maratiia DotigZasii( Baker). A, Longitudinal section of the young sporophyte, showing the distri¬ bution of the vascular bundles, X6; /, leaves; si, stem apex ; r, a root ; f, the foot ; B, young sporo¬ phyte with the prothallium (/r), still persisting. 268 MOSSES AND FERNS CHAP. strongly than the other, so that the latter appears lateral. With the assumption of the pinnate form the leaf also develops the wings or appendages upon the axis between the pinnae. In the fully-developed leaves of the mature sporophyte, the last trace of this is seen in the ultimate branching of the veins, which is always dichotomous. The second root arises close to the base of the second lea , and at first there seems to be one root formed at the base of each of the young leaves ; in the older sporophyte the roots are more numerous. Holle 1 states that this is not the case in Marattia, where only one root is formed for each leaf, in Angiopteris two. This, however, requires confirmation in the older plants. As the roots become larger it is no longer Fig. 140. — A, Longitudinal section ; B, transverse section of roots from older sporophyte of M. Douglasii , showing apparently more than one initial cell, X 200. possible to distinguish certainly a single initial cell. The adjacent segments themselves assume to some extent the function of initials, and thus in place of the single definite apical cell a group of apparently similar initials is formed, which takes its place (Fig. 140). This seems to be in some degree associated with the increase in size of the roots.' According to Holle the four-sided apical cell found in the stem of the young sporophyte is retained permanently, but in Angiopteris this is not the case, as in the older sporophyte a single apical cell is not certainly to be made out. Bower 4 1 Holle (2), p. 217. 2 It is possible that a single initial may be present even here, but the great similarity of the central group of cells makes this exceedingly difficult to determine. 3 Holle, l.c. p. 218. 4 Bower ( 1 1), p. 324. IX MA RA TTIA CExE—ISOE TA CEAE 269 comes to the same conclusion as Holle, although in an earlier paper1 he attributes a single apical cell to the stem of Angi- opteris. The stem in both genera becomes very massive, but its surface is completely covered by the persistent stipules. The arrangement of the bundles is like that of Ophioglossuvi , and they form a hollow cylinder with distinct meshes corre¬ sponding to the position of the leaves. The bundles are, Fig 141 — Marat tia Douglasii (Baker). A, Cross-section of the ultimate rachis of a fully-developed "leaf, X26 ; B, part of the vascular bundle of the same, X200; C, collenchyma from the cortex of the same, X 150 ; D, cross-section of the lamina of the cotyledon, X200 ; xy , xylem. according to Holle,2 concentric, but the phloem more strongly developed upon the outer side. The thick petioles of the full-grown leaves are traversed by very numerous vascular bundles, which at the base give off branches that supply the thick stipules within which they branch and anastomose to form a network. These bundles in Angiopteris are arranged in several circles, or according to De* Vriese and Harting,3 the central ones form a spiral. In the rachis of the last divisions of the leaves, however, both of 1 Bower (2), p. 579- 2 Holle (2), p. 217. 3 De Vriese (1). 270 MOSSES AND FERNS CHAP. Marattia and Angiopteris , there is but a single axial bundle, as in the petiole of the cotyledon. Fig. 142, B show rs a cross-section of a pinnule from a large Fig. 142 .-Angiopteris evccta (Hoffm). A, Part of a leaf with sporangia, X 4 ; B, cross-section of the midrib of the same, X 14 ; col, collenchyma • palisade parenchyma ; C, leaf from a young plant of Marattia Douglasii, showing the stipules (st) ; D, leaflet, with synangia, from a fully-developed leaf of the same species, X4 ; E, horizontal section of a single synangium, X 10. v IX MA RA TTIA CE.E-ISOE TA CEAE 271 leaf of A. evecta, which has much the same structure as that of Marattia. The central vascular bundle is horse-shoe shaped in section, and shows a central mass of large tracheids with reticulate or scalariform markings, surrounded by the phloem made up of very large sieve-tubes much like those of Botrychium, and with these are the ordinary protophloem cells and bast parenchyma. A distinct bundle-sheath is absent, as, according to Holle,1 it is from all the bundles in both Marattia and Angiopteris , except those of the larger roots. The bulk of the ground tissue is composed of large parenchyma cells, but on both sides just below the epidermis is a band of colourless cells which resemble exactly the collenchyma of Phanerogams. In the base of the petiole this becomes harder and forms a colour¬ less sclerenchyma, according to Holle,2 which in Daneea is replaced by brown sclerenchyma like that of the true Ferns. In the lamina of the leaf in Angiopteris too, the arrangement of the tissues is strikingly like that of the typical Angiosperms. A highly-developed palisade parenchyma occupies the upper part of the leaf beneath the epidermis, which bears stomata only on the lower side of the leaf. The rest of the mesophyll is composed of the spongy green parenchyma found in the other Ferns. The smaller veins both here and in Marattia have collateral bundles. The Sporangia The sporangia of the Marattiacese differ most markedly from the Ophioglossacese in being borne on the lower side of the ordinary leaves, and not on special segments. Except in Angiopteris , they form synangia, whose development has only been studied in Marattia .3 Luerssen describes the process thus : “In Marattia the first differentiation of the sporangium begins while the young leaf is still rolled up between the stipules of the next older one. The tissue above the fertile vein is more strongly developed than the adjoining parenchyma, and forms an elevated cushion parallel with the vein. This is the receptacle, which develops two parallel ridges, separated by a cleft. These two ridges grow up until they meet, and their edges grow together and completely close the cleft which lies between. In each half there are differentiated the separate 1 Holle (2), p. 216. 2 Holle (2), ibid. 3 Luerssen (7), vol. i. p. 579. 272 MOSSES AND FERNS CHAP. archesporial groups of cells corresponding to the separate chambers found in the complete synangium.” The whole process takes, according to his account, about six months. Luerssen was unable either in Marattia or Angiopteris to trace back the archesporium to a single cell, which Goebel 1 claims is present in the latter. In Angiopteris the process begins as in Marattia, but at a period when the leaf is almost completely developed and unfolded. The first indication of the young sorus is the formation of an oblong depression above a young vein, and about the border of this are numerous short hairs, which as a rule are absent from the epidermis of the leaf (Fig. 143, A). The placenta is formed as in Marattia, but instead of the two parallel ridges that are found in the latter, the young sporangia arise separately, much as in Botrychium. As in the latter too, Goebel states that the archesporium can be traced to a single hypodermal cell in the axis of the young sporangium. This 1 Goebel (3). IX MA RA TTIA CE.E—ISOE 7 A CE.E 273 cell divides repeatedly, but apparently without any definite order, and the division of the spores follows in the usual way. From the cells about the archesporium tapetal cells are cut off, but these do not disappear, as Goebel 1 asserts, but persist until the sporangium is mature. The growth is greater upon the outer side, which is strongly convex, while the inner face is nearly flat. A section of the nearly full-grown sporangium (Fig. 143, C) shows that the wall upon the outer side is much thicker, and is composed for the most part of three layers of cells, of which the outer in the ripe sporangium have their outer walls strongly thickened. The top of the sporangium and the inner wall are composed of but one layer of cells (exclusive of the tapetum), which are flat and more delicate than those upon the outer side. Near the top on its outer side is a transverse line of cells with thickened darker walls, which project some¬ what above the level of the others. This is the annulus or ring, and resembles closely that of Osmunda. Lining the wall is a layer of very large thin-walled cells which form the tapetum. This in Angiopteris remains intact until the spores are divided. Whether it disappears before the dehiscence of the sporangium was not determined. The contents of these cells, which are very much distended, and evidently actively concerned in the growth of the forming spores, contain very few granules, but are multinucleate in many cases. Whether this condition is due to a coalescence of originally separate cells, or what seems more likely, arises simply from nuclear division in the young tapetal cells, without the formation of cell walls, was not decided. The young spore tetrads, at this time, are embedded in an apparently structureless mucilaginous matter, which stains uniformly with Bismarck-brown. This apparently is secreted by the tapetal cells for the nourishment of the spores. Classificatio?i of Marattiacece The living forms are divisible into three families I. Angiopterideae, with the single genus Angiopteris , and probably only one extremely variable species, A. eveda (Hoffm), which occurs throughout the Eastern tropics. II Marattieae, with two genera, Marattia and Kaulfussia? 1 Goebel (3), 1881, p. 684. 2 Kaulfussia is sometimes made the type of a separate family. T 274 MOSSES AND FERNS CHAP. The former genus includes seven species 1 belonging to the tropics of both the old and new world. The latter includes but a single species, belonging to south-eastern Asia. The synangia are scattered over the lower surface of the palmate leaf, and are circular, with a central space into which the separate loculi open by a slit, as in Marattia. Kaulfussia is characterised by very large pores upon the lower side of the leaf. A study of the development of these shows 2 that at first they are perfectly normal in form, and that the large round opening is a secondary formation, the two guard cells of the young stoma being torn apart, and disappearing almost entirely in the older leaf. III. The Danaeaceae. The single genus Dan a o* w c C- •*' •S. o o o o Z S xx. e _ - ? $ bo cs ‘3a 0 « s V X ' - Q _T : CJ ^ c : « "aJ : ° £ l- rC ! x-s £ ■ . _r o P* ; ^ E w . o c I 5